Anniversary Address of the President, Charles Knight, F.R.C.S.
Charles Knight, F.R.C.S., President, in the chair.
New members.—E. F. Burrell, George M. Wink, C.E., Hon. William Fox, M.H.R., Alexander Kerr, F.R.G.S., Alexander McKay, Thomas Kirk, F.L.S., Charles Holmes Borlase, John Newton Coleridge.
Before the business of the evening was formally entered upon, Dr. Hector introduced to the society Dr. Berggren, of the University of Lund, who is at present engaged in making a botanical exploration of New Zealand, and Mr. Joseph Holloway, agent for the Agricultural Labourers' Union, who is making a tour of observation through the various Provinces for the purpose of furnishing a report upon the suitability of New Zealand as a field for immigration.
Publications received from Harvard College, the Smithsonian Institution, and the Geological Society of Florence were laid on the table.
There were also laid on the table a number of marine specimens, presented to the Colonial Museum by the gentlemen belonging to the “Challenger” expedition, and a microscope with mounted slides for showing the nature of the bottom of the sea between New Zealand and Australia, as evidenced by specimens obtained from the soundings made by the “Challenger.”
The President delivered the following anniversary
It has been the custom for your Presidents in their annual address to notice the papers discussed at the Society's meetings during the year. I find it difficult to make such notices interesting. Indeed, it is the most valuable papers that are the most difficult to comment on, except in general terms of praise. Take Mr. George's paper on the Patent Slip at Evans Bay—the first of our papers in the Transactions of the Institute—it is over-running with valuable suggestions for engineers; or turn to the end of the volume, we have Captain Moresby's Lecture on New Guinea; certainly in this last case I may tell you that Dr. Macleay visited the Astrolabe Gulf in the years 1871 and 1872, and studied the inhabitants of the whole coast of that Gulf, and the dwellers on the islands near Cape Duperré, and speaks of them, as Captain
Moresby did of those he met, as living a life of such perfect happiness that he called the islands “The Archipelago of Contentment.” As regards the characteristics of races, it may be interesting to note, in connection with Captain Moresby's description, that the Papuans have the upper teeth projecting considerably beyond those of the lower jaw, and, contrary to what is usually stated, there is no such, roughness of the skin as would constitute a race characteristic. The colour of the skin, too, is in general of a chocolate brown—not of a bluish-black colour, as has been previously asserted; and the hair of the head is not naturally disposed in tufts or clumps, but grows just as it would upon the head of a European. Mr. Galton, from whose review I have culled the above remarks, completes the picture by observing that the Papuan maidens begin, even at the tender age of seven years, to cultivate the art of which Mr. Turveydrop was the distinguished professor.
You will find at page 391 of the Transactions for 1873, a short notice of a discussion on Solar and Terrestrial Radiation, introduced by Mr. C. R. Marten, who explained that the black bulb thermometer in Southland frequently ranged as high as 170°, being 30° higher than in Sydney, and much higher than it has ever reached in the North Island.
As some doubts are implied in the printed report of the correctness of the readings, I wish to state that Mr. Marten is not only an enthusiast in meteorological pursuits, but a most painstaking observer, with whom my duties as first Director of Meteorological Stations in New Zealand brought me in very pleasing communication. As this is a subject on which I formerly took much trouble, and may claim-for myself the merit of having established all the principal Meteorological Stations in New Zealand, and as it was a great comfort to have the co-operation of Mr. Marten, I am anxious to explain why I believe the observations referred to are correct. Of course we all know how difficult it is to prevent “cooking” of observations. In looking over my correspondence with a distinguished savant who had a great deal to do with getting up meteorology in India, he notices how discouraging it was to work at the results of people who had no training in the use of instruments. The stupidity of some observers is impregnable. An intelligent, well-educated man supplied him a long series of wet-bulb observations obtained by holding a thermometer under water and reading off—the bulb was wet, what more could be wanted! You will understand, then, the comfort, in starting a number of Meteorological Stations, of having a Member of the Meteorological Society of England for a coadjutor.
I did not join in the discussion further than to inquire what was the vapour tension at the time those high indications of the black bulb thermometer were taken. I shall explain why I asked for that information.
The black bulb thermometer is always exposed, for observation, to the
direct rays of the sum. The calorific rays of the sun pass through- air devoid of aqueous vapour with no appreciable loss; but if water in the form of invisible vapour be present, the air is not perfectly transparent to those rays, and offers, I believe, a slight obstruction to their passage. It is almost opaque to radiant heat from the surface of the ground. Transparency to heat and light is witnessed in the passage of the sun's rays through the glass windows of our dwellings. The heat in a close room into which the sun shines may be overpowering, while the glass, through which the whole of the heat has passed, remains cold. The greater the proportion of aqueous vapour the more solar heat is absorbed in its transit through the atmosphere. Now, the quantity of vapour in the air depends mainly on temperature. In the colder regions of the south, although the air may be saturated with vapour, the relative proportion of vapour to air is much less than in tropical climates; and thus it happens that in Southland less of the sun's heat is lost in its passage to the earth. For instance,—the quantity of vapour in air at a temperature of 90° Fahr. is four times as great as in air at 50° Fahr.; and the consequence of its being loaded with vapour at the higher temperature is a slight obstruction of the passage of the sun's rays; and were it not that they strike in Southland with a somewhat greater obliquity than in Sydney, and thus traverse a greater mass of air, it is possible that these high readings of the black bulb thermometer would more frequently happen in the southern parts of the South Island.
Dr. Hooker, in his observations on the climate of the Himalayas, states that at a height of 10,000 feet at 9 a.m. in the middle of summer the thermometer mounted to 132° Fahr. in the sun when the temperature of the air was 32° Fahr., a difference of 100°. This difference, no doubt, would have been much greater had the black bulb been protected from currents of the surrounding cold air, and had it laid on a bed of black cotton-wool. Tyndall quotes this for the purpose of showing that the extraordinary difference of 100° can only be accounted for by the sun's rays passing through air almost devoid of aqueous vapour as through a vacuum. Dr. Hooker found the same extraordinary difference on the plains of India, because of the dryness of the air; but no such result had been found in Calcutta, where the heated atmosphere is surcharged with aqueous vapour. Tyndall goes on to say that he himself “never, under any circumstances, suffered so much from heat as in descending on a sunny day from the Corridor to the Grand Plateau of Mont Blanc. The air was perfectly still, and the sun literally blazed against him and his friend. Though hip deep in snow, still the heat was unendurable.”
What I contend for is, that in high latitudes the air does not contain the same quantity of aqueous vapour as in warmer latitudes. That the presence of aqueous vapour interferes in a slight degree with the passage of solar heat,
and this slight obstruction affects the black bulb so as on rare occasions to render the readings no higher in Sydney that in Southland. And I may add, as a “rider” to the above, that those who contend that the atmosphere, whether charged with vapour or not, is a vacuum to the sun's heat rays, are left with no explanation of the heat being diminished when that luminary is low down in the heavens.
In connection with the Meteorology of New Zealand, I wish to offer an explanation of the Hot Winds of the Canterbury Plains. The N.W. dry, hot winds of Australia, in their passage over the ocean, become surcharged with vapour at the expense of a noticeable part of their heat. In the philosophic language of the day, the heat of the air is made to do work by converting water into vapour, and by maintaining it in that state. The sensible heat thus absorbed by vapour is converted into latent heat—that is, the heat is not lost, but is engaged in the veiled work of maintaining water in an invisible state. The air in thus dissolving water becomes a carrier, or distributor of heat. It is not difficult to give an approximate estimate of the quantity of heat made sensible to the thermometer by the reconversion of vapour into water. The problem has been solved by experiments, and it is found that the amount of heat stored up in aqueous vapours from one pound of water is sufficient to heat 1000 pounds of water one degree of Fahrenheit, or, as Tyndall puts it, to fuse five pounds of cast iron.
Next as to the phenomena arising out of the fall of heavy rains on the flanks of the ranges on the West Coast. The quantity of heat liberated would be considerable did not other causes interfere with its escape. The rain itself carries down with it a small part of the sensible heat, but the greater portion of that set free is at once taken up by the atmosphere in rising to the altitude of the lofty ranges in its passage to the plains of the South Island. The sudden rarefaction is due to the loss of pressure of the column of air lying between the level of the sea and the average height of the ranges. This dilatation is accompanied by what used to be termed an increased capacity for heat, so that heat is absorbed by the air itself. This too, in the current phraseology of the day, is called work done at the expense of heat. So that altogether we have a diminution of sensible heat, but not an actual loss of heat, by the passage of the air over the ocean, and next by the rarefaction of air in its ascent to the higher regions of the ranges. When air expands by reason of the loss of pressure, the undulations of the molecules of air which we term heat, diminish also—or, in other words, the amplitude of the vibrations is diminished, and the distance between the undulations increased. Motion imposed on the molecules of matter would go on for ever, just as any motion imposed on a mass would never cease, if there were no medium through which it could communicate its motion to other bodies, or in some other way exhaust
itself. This inertia belongs to molecules as much as to masses. While the swing of the molecules is diminished, and the distance between the undulations is increased, the actual force, which we call heat, remains undiminished. It is only necessary that the undulations should be again crowded together in order that the energy may be restored.
So far I hope that I have made my meaning clear,—that air in taking up moisture loses sensible heat. No one who has travelled on the West Coast of the South Island can have failed to notice when he leaves the forest road, and comes on the dreary sands of the coast, with a moderate sea breeze, how miserably cold the air is in the immediate vicinity of the breakers. This is owing to absorption of sensible heat by the solution of the spray in the current of air sweeping over the sea.
Next, in reference to the heat gained, if any, in the passage of the air over the extensive elevated region between the West Coast and the Canterbury Plains. The air on the mountain ranges gains no addition of temperature from the direct radiant heat of the sun, for the rarefied air is, to use a technical expression, almost transparent to the sun's heat rays—it permits them to pass with very slight loss. The sun warms the ground but not the air. It is not so, however, with the heat radiating from the surface of the ground—this is almost entirely absorbed by the atmosphere, which thus gains sensible heat until at length it reaches the eastern slopes of the mountain ranges.
Here, where the column of air begins its descent to the plains, we ought to have a complete reversal of every phenomenon that accompanied its passsage from the level of the sea on the West Coast till it reaches the elevation of the mountain ranges. As the column of air sinks down, the increased extent of the vertical column gives increased pressure, and compresses more and more the lower stratum—the latent heat becomes sensible and the thermometer rises. But it is necessary that I should give you here some proof that increased pressure adds to the energy of heat in aeriform bodies, or, in the old expressive phraseology, converts the latent heat into heat recognised by our senses, and registered by the thermometer. Airy has explained that when the changes of volume and pressure are very rapid, the changes of temperature of the air are very great:—“Upon suddenly condensing air it becomes very hot. We have verified the experiment, that if inflammable tinder is placed in the bottom of a cylinder in which a piston fits tightly and slides easily, when the piston is driven rapidly down so as to condense the air very much before it has time to impart the whole of its heat to the surrounding metal, the air will inflame the tinder.” And Airy remarked, “in the powerful air pumps (driven by large steam engines) which were used to exhaust the air tubes upon the atmospheric railway, that when the attenuated air in the tube, having acquired the temperature of the ground, was compressed by the operation of pumping
so as to be able to open the last valve in opposition to the pressure of the atmospheric air, the emergent air was so hot as to be unbearable to the hand. If the heated air, without having lost caloric, be allowed to expand to its former dimensions it exhibits its former temperature; that is, it cools by sudden expansion. And this is so well known that it has been proposed to supply apartments in hot climates with cool air, by compressing air in a close vessel, allowing the increased heat to escape by contact of the vessel with the external air or neighbouring substances, and then permitting the condensed air (at the atmospheric temperature) to expand into the apartments, when it would have a much lower temperature.”
You see at once that the condition of the air in the tubes of the atmospheric railway bears the closest relationship to what takes place in the transit of the air from the West to the East Coast. First, the rarefaction of air in the tubes;—this represents the expansion of air in its ascent to the mountain ranges. The subsequent compression of air, for raising the escape valve is analogous to the descent of the column of air from the ranges;—and the escape of the hot air at the valvular opening is a counterpart of the heated air sweeping over the Canterbury plains.
A paper on the Preservation and Treatment of the Timber of New Zealand, by Mr. Buchanan, of the Geological Survey Department, is deserving of some notice.
The forests of New Zealand are cut down recklessly at all seasons of the year; and when the trees are sawn into square timber or planks no attempt is made to preserve them against decay or deterioration.
Greater attention should be paid to seasoning. I am doubtful whether we do not, however, attach too great importance to the time of the year in which the trees are felled. If cut down in summer they should be allowed to lie where they are felled, and no branches cut off, so that the sap may be dried off by evaporation from the surface of the leaves. Unless this be attended to, the timber from trees cut down in summer, and immediately sawn up, will be much deteriorated in value—the planks will warp and the larger timber will split and spoil from hasty drying.
On the whole, it is safer that the trees should be cut down, or killed by “ringing,” during the winter months. As soon as possible after being felled they should be cut into square timber and planks, and these stacked in a proper manner, and carefully protected from the sun's rays.
Timber so cut, seasoned, and protected, might be branded as a guarantee to purchasers. The letter of the brand would show the year in which the timber was felled, just as silver plate is lettered to show the year in which it was stamped.
With respect to ringing trees which exude large quantities of gum from
the cut surfaces, I am decidedly of opinion that the loss of gum would be followed by a loss of power in the timber to resist decay, and that in such instances “ringing” is objectionable.
One great advantage of charring the lower end of posts is that the sap is dispersed at that end. If, in addition to charring, the heated end is immediately plunged into cold tar, made more liquid by the addition of kerosene, I think the post below the ground would be almost indestructible. The moisture left in the charred end, when the post is first removed from the fire, would be in form of steam, and on its condensation by the cold of the tar bath in which it is plunged would produce a vacuum into which the tar would be forced by atmospheric pressure.
I may mention that careful experiments have been made in the United States of America by Generals Cram and Gillmore, and the result of their investigations is, that Seely's process is the best. It consists in subjecting the wood to a temperature above the boiling point of water and below 300° Fahr., while immersed in a bath of creosote a sufficient length of time to expel the moisture. When water is thus expelled the pores contain only steam; the hot oil is then quickly replaced by a bath of cold oil, by means of which change the steam in the pores of the wood is condensed and a vacancy formed, into which the oil is forced by atmospheric pressure and capillary attraction.
I find that in California they are already alarmed at the rapid destruction of their forests, containing the largest and finest trees in the world. It is estimated that one-third of all the available timber has been consumed, and that the whole of the available timber will be consumed in twenty years. One of the worst features of the settlement of new countries is the reckless way in which the timber is destroyed. Not only is the practice condemned in severe terms by thoughtful men in California, but the opinion must be gaining ground that the State should interfere. The only remedy seems to them to be for the Legislature to take up the matter, and by proper laws to provide not only for the preservation of the forests, but for the planting of trees pari passu with the settlement of the country.
It is maintained by writers on the subject in America, that at least one-third of the surface of any country should be forest—that this proportion between clear land and forest is one which will secure the greatest results in an economic point of view. It is also insisted upon that a fertile country, if stripped of its forests, may be half overwhelmed by desolation from the consequent change of climate. That, in fact, a country so denuded of rain-gatherers is either dried up in summer or the soil is washed off from the hillsides by the heavy rains of winter. Marsh, speaking of the destruction of forests upon the different countries of the earth, says:—“There are parts of
Asia Minor, of Northern Africa, of Greece, and even of Alpine Europe where the operation of causes set in action by man has brought the face of the earth to a desolation almost as complete as that of the moon. The destructive changes occasioned by the agency of man upon the flanks of the Alps, the Apennines, the Pyrenees, and other mountain regions in Central and Southern Europe, and the progress of physical deterioration, have become so rapid that in some localities a single generation has witnessed the beginning and the end of the melancholy revolution.”
I know no sight more sad than to witness the destruction by fire of forests on the hill-sides—those mournful streaks sweeping along the more accessible sides of the ranges, with blackened trunks like Banquo's ghosts here and there in the midst—without parallel the most melancholy spectacle of wasteful destruction. I have doubts of the probability of much immediate good being effected in the way of planting in the permanent settled districts of the Colony. But there can be no doubt of our power to stay the destruction of forests on the ranges and on other lands not well adapted for agriculture. Here we have unquestionable means not only of staying wanton destruction, but of securing the successional growth of trees to make good the full grown timber when removed. To plant land with valuable timber is a slow process—to preserve what we have is surely our duty. It is on the ranges and highly broken ground that the timber is most effective in ameliorating a climate and of feeding the streams from which the plains may be irrigated.
The most interesting of our papers is that by Dr. Hector on the huge Fossil Reptilian Remains lately discovered in the South Island. That memoir has a value for all time. As a contribution to the knowledge of those enormous reptiles it will certainly engage the careful study of scientific men both in Europe and North America. Contemporaneous with these discoveries we find, from the report of Cope, that similar skeletons of these monsters of the ancient seas are being found in the cretaceous strata of the Kansas, in North America.
“If the explorer of these plains” (on whose level surface, denuded of soil, may be found huge oyster shells not less than two feet across, some opened, like remnants of a half-finished meal of some titanic race, who had been frightened from the board never to return) “searches the ravine he will,” says Cope, “come upon the fragment of a tooth or jaw, and will generally find a line of such pieces leading to an elevated position on the bank, where lies the skeleton of some monster of the ancient sea. He may find the vertebral column running far into the limestone that locks him in his last prison; or a paddle extended on the slope as though entreating aid; or a pair of jaws lined with horrid teeth, which grin despair on enemies they are helpless to resist; or he may find a conic mound on whose apex glisten in
the sun the bleached bones of one whose last office has been to preserve from destruction the friendly soil on which he reposed.”
The Leiodons, parts of whose skeletons are seen in our Museum, were of enormous length, varying from thirty to one hundred feet; “their heads were large, with eyes partly directed upwards; they were furnished with two pairs of paddles like the flippers of a whale; they were furnished with formidable teeth for seizing their prey.” The physiognomy of the giant species in our collection was rendered peculiar by a long projecting muzzle. Cope once found the “wreck of an individual of the Leiodon proriger strewn around a sunny knoll beside a bluff, and his conic snout pointing to the heavens formed a fitting monument, as at once his favourite weapon and the mark distinguishing all his race.” And here I must quote from Cope a peculiarity of these creatures by which they are unique among animals, but which I do not see alluded to in Dr. Hector's elaborate report. Nor can I satisfy myself that it could have existed in the reptiles whose fossil remains are in our Museum:—“In swallowing their prey like snakes, they were without that wonderful expansibility of throat, due in the latter to an arrangement of levers supporting the lower jaw. Instead of this each half of the lower jaw was jointed nearly half way between the ear and the chin. This enabled the jaw to make an angle outwards, and so to widen by much the space enclosed between it and its fellow. The ends of these bones were in the Pythonomorpha only bound by flexible ligaments. The outward movement of the basal half of the jaw necessarily twists in the same direction the ‘quadrate’ or column-like bone to which it is suspended. The peculiar shape of the joint by which the ‘quadrate’ bone is attached to the skull depends on the degree of twist to be permitted, and, therefore, to the degree of expansion of which the jaws were capable. As this differs much in the different species, they are readily distinguished by the ‘quadrate’ bone when found. There are some curious consequences of this structure, and they are explained as an instance of the mode of the reconstruction of extinct animals from slight materials. The habit of swallowing large bodies between the branches of the under jaw necessitates the prolongation forward of the mouth of the gullet; hence the throat of the Pythonomorpha must have been loose and almost as baggy as a pelican's. And the tongue,” continues Cope, “must have been long and forked, and for this reason its position was still anterior to the glottis, so that there was no space for it except it were enclosed in a sheath beneath the windpipe when at rest, or thrown out beyond the jaws when in motion. Such is the arrangement in the nearest living forms, and it is always in these cases cylindrical and forked.”
The Transactions of the New Zealand Institute show by numerous papers how actively the minds of our geological friends are engaged on the subject of
the Glacial Period. It is the fashion of the philosophy of the day to ascribe much of the moulding of our hills and valleys to the denuding power of ice— more in fact than one is inclined to admit.
Professor Phillips, at a late meeting of the British Association, remarked that one is almost frozen to silence in presence of the vast sheets of ice which some of his friends, followers of Agassiz, believe themselves to have traced over the mountains and vales of a great part of the United Kingdom. He refuses to accept the proposition that these “ice-rubbers” plough out the valleys and lakes, until we possess more knowledge than has yet been attained regarding the resistance offered by ice to a-crushing force, seeing that under a column of its own substance 1000 feet high it would not retain its solidity.
I have alluded to Phillips' opinion, because I see in Geikie's late work that reference is made to the fact that from the foot of glaciers in Greenland streams of water issue and unite to form considerable rivers, one of which, after a course of forty miles, enters the sea with a mouth nearly three-quarters of a mile in breadth—the water flowing freely at a time when the outside sea was thickly covered with ice.
This flow of water, Geikie thinks, probably circulates to some extent below every glacier, and he accounts for it by the liquefaction of ice from the warmth of the underlying soil. I am sure you will find a more natural solution of this flow of water from glaciers—estimated not less than 3000 feet thick—in the suggestion first made by Professor James Thomson, and subsequently proved by his brother, Professor W. Thomson, that the freezing point of water is lowered by the effect of pressure 0.23° Fahr., or about a quarter of a degree for each additional atmosphere of pressure. Now, a sheet of ice 3000 feet thick is equal to a pressure of eighty-three atmospheres, at which pressure it would require a temperature of 19° below freezing point to retain the form of ice. In the state of running water below the glacier, it might readily, as Geikie states, absorb heat from the underlying soil sufficient to retain its liquid form, as the overlying weight gradually lessened at the edge of the glacier. In this, too, we have a safe assurance that these enormous thicknesses of glaciers can exist only where there is scarcely any or no inclination of the land to the sea board, and that no sheets of ice of such enormous thickness could possibly exist on the sides of mountains, as they would have between them and the mountain side a stratum of water; and, to use a common expression, would come down “ on the run.”
And this may well make us hesitate to adopt with Geikie the views of the Swiss glacialists, who, I gather from Geikie's late work, speak of sheets of ice having existed in the great Ice Age not less than 3000 feet thick, overtopping the Jura, and stretched continuously from the Rhine Valley; and Geikie adds,
that no one can believe that this great glacier stopped on the banks of the Rhine.
I do not deny that sheets of ice 3000 or 5000 feet thick exist. I shall maintain, however, as an established fact, that ice if at the temperature of 32° Fahr. throughout cannot support a column of its own substance 3000 feet high. Nevertheless, a 3000 feet sheet may exist, although the temperature at the surface of the ice is only 32° Fahr., but in this case the temperature at the base cannot be higher than 13° Fahr. I will explain myself. The specific heat of water is far greater than ice. One pound of ice at 32° Fahr. mixed with one pound of boiling water gives two pounds of water at 51°; so that seventy-one degrees of heat have been lost in the mere conversion of ice into water. We thus see that every pound of ice converted by pressure into water demands a large supply of caloric, as a necessity of its change of condition, and absorbs it instantly from the ice in contact with it above. The ice in the immediate vicinity of the layer of water, hardened by loss of caloric, stops for the moment the further conversion of ice into water. But this state of matters continues only momentarily, the ice below, in its turn, robs the ice above of caloric, and this softened is unable any longer to bear the pressure, and flows away as water; and so the process extends, until a regular gradation of temperature is progressively but uninterruptedly established throughout the mass, and an equilibrium formed between the forces by which the sheet of ice maintains a fixed altitude. That is, we shall have a gradual fall of temperature from 32° on the surface to 13° at the base, the latter degree being the temperature at which ice will sustain a column of 3000 feet. I further maintain that no such column as 3000 feet can continue at that height for an indefinite time, unless the temperature of the air is much lower than 32°, because the temperature, if higher than 13°, would gradually creep down to the base of the column of ice, where the lowest stratum would continually melt away in the form of running water.
And we thus see, as a necessity of the case, that all thick glaciers have running streams at their foot.
I have brought this under your notice this evening, because no satisfactory explanation has hitherto been given of the cause of running water at the foot of glaciers, nor how it is that sheets of ice 3000 or 5000 feet thick are enabled temporarily to maintain their thickness.
Dr. Haast, Mr. Travers, and Captain Hutton have given much interest to the subject. The origin and formation of the Canterbury plains have led to the discussion.
Captain Hutton has come to the conclusion that the formation of the Canterbury plains is due to the action of the sea. His argument is, that the plains rise gradually from the sea board with a gentle slope—that in places
they warp round the spurs of the hills at the same level—and that no engineering power could form such level and extensive plains with their beds of water-worn shingle but the ocean itself—that the singular fact that the Hurunui and Canterbury plains are on the same level, is, in his opinion, an irresistible proof of the correctness of his views. I need scarcely add that if this view be correct there has been an elevation of the land of about 2000 feet.
Dr. Haast, on the other hand, assumes as sufficient for his views that glaciers of enormous size have moved down from the mountain ranges, and ploughed from the mountain sides the drift with which they have covered the more insignificant hills and formed the plains—that when the glacier outlets ceased to flow and to deposit any more boulders and gravel, the rivers cut through the deposits until they reached the harder rock on which the deposits reposed.
The necessities of this explanation require the admission that a glacial period formerly existed in the southern hemisphere—such as is generally admitted to have once existed in the northern hemisphere.
The weak point of Haast's theory is, that it does not account for the distribution of the drift so as to form regular plains. It seems to me impossible to confound the irregular pell-mell deposition of glacial drift with the evident stratification, through the agency of water, which exists in the Canterbury plains. And I observe that Jukes, speaking of the glacial deposits in the lowlands of Scotland and Ireland, and in the northern parts of England, even as far south as the northern margin of the Thames Valley, states that he has not the slighest doubt that they were stratified under the sea, notwithstanding the absence of sea shells from the greater part of them.
Mr. Travers objects to Dr. Haast's assumption of a glacial period, because of its remarkable character, and because we have no evidence whatever that such a change of climate as this supposes ever took place. Mr. Travers thinks it more reasonable to conclude that a great elevation of the South Island above its present level would give a climate sufficiently cold. An elevation of the South Island of about 4000 or 5000 feet would, in Mr. Travers' opinion, give a climate quite as cold as that assumed for the glacial epoch.
The exigencies of these theories require either a change of climate to something like the cold of Greenland, which would satisfy Dr. Haast's requirements, or a great elevation of the land. Of course, when we use imagination in scientific matters we have sometimes to draw liberally on nature for support; and Mr. Travers' theory has an elasticity about it, for, if we object to an elevation of 5000 feet as insufficient, we might double the elevation without being unreasonable.
The strength of Captain Hutton's views springs out of the fact that he
summons to his aid the great leveller and engineer—the sea, with its never-ceasing waves grinding the rocks into sand, and fashioning the boulders, and assorting the materials brought to it, either by the glaciers themselves or by the rivers flowing from the mountain ranges, and spreading them out in vast plains. Everything seems to show that plains of any extent are the result of the action of the ocean, or of vast inland seas. I do not question the statement that terminal moraines attain great size, and form mounds of rough angular fragments and débris—perhaps some hundreds of feet in height. These are the wastes of the mountains. What I contend for is, that nowhere is this confused débris scattered far and wide and levelled out into strata, forming plains of great extent by the action of glaciers. Captain Hutton admits that the glaciers of the South Island have been at some former time of much larger dimensions than they are at present, and that there may have been a glacial epoch in the southern hemisphere. But he does not admit that such an epoch bears any relation to, or was contemporaneous with, that of Europe. He would refer it, if it ever existed at all, to a period long antecedent. At the same time he guards himself by stating that we have no proof of a change of climate; and, as he considers an elevation of the land of about 3000 feet would be able by itself to account for a great extension of the glacier system, there is no necessity of calling in the aid of any other cause.
The existence of a glacial epoch must not be denied here. It is a settled question among geologists that many of the changes on the earth's surface are due to it. If I am not encroaching too much on your patience, I will explain why I do not think we are justified in objecting to Dr. Haast's assumption of a glacial epoch in the southern hemisphere on the ground that it is of a very remarkable character, and as being supported by no evidence whatever; at any rate he follows in the wake of great men. We find Professor Agassiz startling the geological world by his strong opinion that a gigantic glacier once filled the entire valley of the Amazon, and he invited the members of the Alpine Club to go out and search for traces of glacial action on the mountains of Ceaná; and I see by a notice in “Science Gossip” that on his South American Expedition he discovered evidences of glacial action on a scale so extensive as to more than suggest that the southern hemisphere has under-gone a similar general glaciation to that of the northern. The glaciation has been traced as far as the northern end of Chiloe Island. The Professor believes that during the glacial period the two hemispheres were capped with a sheet of ice of enormous thickness. Ancient moraines abound in South American valleys; and in the Straits of Magellan one was found damming up a valley.
But, as I said before, we must not overstate the action of ancient glaciers. I see that Dr. Hector, in his address last year, states that the mountain ice-cap
performs its work of eroding the elevated rock mass into ridges and peaks; and that after the first rough excavation has been performed, and only the hard cores of crystalline or tough metamorphic rocks have survived the denudation, and when the valleys have all been perfectly moulded to perform their functions of ice gutters, then the process is admitted to be very slow. But to ascribe thus to glacier action the formation of the very ridges and peaks of mountain tops is, I think, unreasonable. In fact no larger amount of work can be assigned to glaciers even of the glacial epoch, as the Duke of Argyle remarks in a quotation made by Mr. Travers, than that of deepening the valleys which existed before—that on the one hand when the period began it found the existing system of hills and valleys in the main determined, and on the other that it cannot have left them exactly as it found them. But this is very far from the view which Dr. Hector would seem to maintain—that mountain and valley, with all their characteristic variety of surface, have been cut out of the solid by enormous glaciers. Now, the very opposite is the case. It is the pre-existing configuration of hill and valley and mountain range which has determined the movements of these glaciers, so that, as the Duke of Argyle says, the effects of glacial denudation become a comparatively narrow question.
But whether we ascribe too much or too little to the existence of a glacial epoch, let us for a moment consider what are the probable causes which might explain the extraordinary changes of climate which have certainly existed in the earth in very distant epochs of time.
There are two sources of heat which have varied greatly—the heat of the sun and heat from the body of the earth itself.
Our faculties can form no conception, and can make no answer to the question, how far the forces which are in activity in the sun have exhausted themselves. Say that such changes can be worked out in any length of time that can be assigned; such period, however vast, is nothing to eternity. To eternity no limit is assignable; priest and philosopher alike are ignorant here. But though we can give no answer to the question, we are assured that the forces which are in activity in the sun as revealed to us by light, “the winged messenger,” through the spectroscope, are forces operating on the same substances as those which form the earth; that they must have had a beginning, as assuredly they will have an end; and that the sun will in the course of time cease to evolve heat, light, and electricity. It seems certain that they vary greatly in their intensity—at one epoch the heat of the sun may have been much greater than it is now, and at another far less. It is impossible they can have always been the same.
I have dwelt longer on this subject than I should have done, had I not been desirous of introducing to your notice the very plausible theory of
Mr. Croll—a theory rendered more interesting because Darwin has used it to explain facts in connection with, the distribution of plants and animals, and because it involves the admission that a glacial period existed in the southern hemisphere, but at a period of about 13,000 years, or some multiple of that time, prior to the northern epoch. This, again, is in support of Captain Hutton's views, who, with his usual caution, states that if he were to adopt the opinion that a glacial epoch once existed in the southern hemisphere, it would be with the distinct understanding that it was far anterior to the pleistocene period—that is, anterior to the northern epoch.
In giving you an epitome of Croll's views, I shall, with slight exceptions, use his own words.
Croll's theory is based on the assumption that during the glacial period the eccentricity of the Earth's orbit was at least double what exists at present, but not so great by far as the eccentricity of the orbit of the planet Mars. This supposition does not involve any increase in the mean distance of the Earth from the Sun, nor in the period of revolution—both of these elements of our orbit are absolutely unchangeable.
The first step in Croll's argument is that ocean currents are produced by winds; that the main ocean currents agree with the direction of the prevailing winds, as may at once be seen by comparing the direction and paths of the prevailing winds, shown in Messrs. Johnston's small Physical Atlas, with the ocean currents as shown in the Current Chart published by the Admiralty. Of course the conformation of sea and land partially interferes with this agreement, but the principal currents of air and of water agree precisely. There is nothing new or extravagant in this. The younger Herschell vindicates to the winds their supremacy in the production of ocean currents. If, says Herschell, there were no wind there would be no Gulf Stream, or any other considerable oceanic current.
Croll next shows that oceanic currents are the great distributors of heat over the globe. Taking for instance the Gulf Stream, he calculates the amount of heat conveyed as so enormous as to be equal to one-fourth of all the heat received from the sun by the Atlantic Ocean from the Tropic of Cancer up to the Arctic Circle; and were it not for the Gulf Stream, and other ocean currents, only a small portion of the globe would be suited to the present order of sentient beings; that London, instead of possessing a mean annual temperature of nearly 50°, would have a mean temperature of not over 10°. Of this enormous amount of heat one-half is derived from the southern hemisphere by means of ocean currents. Without such transference of heat it would be impossible to account for the North Atlantic being 5° warmer than the South Atlantic. This current from the south is owing to the superior strength of the S.E. trades.
We thus see that Croll's argument is based on two facts, which he considers placed beyond all doubt—that winds are the impelling cause of ocean currents, and that the ocean currents are the great agents employed in distributing over the globe the excess of heat received by the sea in intertropical regions.
The majestic flow of waters from the Gulf of Mexico—that “mighty river,” as Maury terms it—equals in magnitude a current of at least forty miles broad and 1000 feet deep, flowing at the rate of two miles an hour, and conveys a quantity of heat equal—to use the philosophic slang of the day—to 77,479,650,000,000,000,000 foot-pounds. That he has not overestimated either the temperature or the volume of the Gulf Stream is shown by the important results obtained during the “Challenger” expedition. Between Bermuda and Sandy Hook the stream is sixty miles broad and 600 feet deep, with a maximum velocity of from three and a half to four miles an hour; while the observations made between St. Thomas and Sandy Hook reveal the existence of an immense flow of warm water 2300 feet deep, coming either from the Gulf of Mexico or from the Caribbean Sea. At Sandy Hook it extends 1200 feet deeper than the Gulf Stream itself. This mass of water, after travelling northwards for about 1000 miles, crosses the Atlantic in the direction of the Azores, where it appears to thin out.
Croll then goes on to argue that any cause which will greatly affect the currents, or greatly change their paths and mode of distribution, will of necessity greatly affect the climatic condition of the globe. But, as the existence of these currents depends on the winds, any cause which will greatly affect the winds will also greatly affect the currents, and consequently will influence the climatic conditions of the globe. Again, as the existence of the winds depends mainly on the difference of temperature between equatorial and polar regions, any cause which will greatly affect this difference of temperature will likewise greatly affect the winds. That is, should any cause increase the difference of temperature between the equator and the pole on the one hemisphere, and decrease that difference on the other hemisphere, it would effect a change in the distribution of the aerial currents, which change would in turn produce a corresponding change in the distribution of ocean currents.
Now, an increase in the eccentricity of the earth's orbit tends to lower the temperature of one hemisphere and to raise the temperature of the other. Let us imagine the eccentricity at its superior limit to be .07775, and the winter solstice of the northern hemisphere, instead of in perihelio as at present, to be in aphelio. The midwinter temperature, owing to the increased distance of the sun, would be lowered enormously; and the effect of this would be to cause all the moisture which now falls as rain during winter in temperate
regions to fall as snow. Nor is this all; the winters would not merely be colder than now, but they would be also much longer. At present the summer half-year in the northern hemisphere exceeds the winter half-year by nearly eight days; but at the period in question, supposing the eccentricity of the earth's orbit increased, the winters would be longer than the summers by upwards of thirty-six days. The heat of the sun during the short summer would not be sufficient to melt the snow of winter, so that gradually year by year the snow would continue to accumulate on the ground. At the same time it is quite true that an increase of eccentricity does not give more solar heat to the one hemisphere than to the other, but, nevertheless, it would bring about a different state of things.
On the southern hemisphere the opposite condition of things would obtain. Owing to the nearness of the sun during the winter of that hemisphere, the moisture of the air would be precipitated as rains in regions where at present it falls as snow. This and the shortness of the winter would tend to produce a decrease in the quantity of snow. Thus you will observe that the difference of temperature between the temperate and polar regions would be greater on the northern than on the southern hemisphere, and as a consequence the aerial currents of the northern hemisphere would be stronger than those of the latter. This would be more especially the case with the trade winds. The N.E. trade winds, being stronger than the S.E. trades, would blow across the equator, and thus the equatorial waters, driven by the winds, would be impelled more to the southern than to the northern hemisphere, and the warm water carried over to the southern hemisphere would tend to increase the difference of temperature between the two hemispheres. And it was this mutual reaction of those physical agents which led to that extraordinary condition of climate in the northern hemisphere which prevailed during the glacial epoch.
At present the S.E. trades are the stronger, and sometimes extend to 10° or 15° north of the equator; so that the mean position of the median line lies at least 6° or 7dG north. But if Croll's views be adopted, the N.E. trades blowing across the equator, the median line would be shifted considerably to the south of the equator. The effect of this shifting the median line between the N.E. and the S.E. trades from the northern to the southern side of the equator, and with it the equatorial current of the Atlantic, would be that the whole of the waters would strike obliquely against the Brazilian coast, and thus be deflected into the Southern Ocean. The effect produced on the climate of the North Atlantic and North-Western Europe by the withdrawal of the water forming the Gulf Stream may be conceived from what has already been stated concerning the amount of heat conveyed by that stream. The heat thus withdrawn from the North Atlantic would go to raise the
temperature of the Southern Ocean and Antarctic regions, and a similar result would take place in the Pacific Ocean.
In the regular course of events the long axis of the earth's orbit would shift, and in about 12,934 years the winter solstice of the southern hemisphere would be in the aphelion, and in New Zealand the glacial epoch would be at its maximum, while in the northern hemisphere the great Gulf Stream, together with the flow of southern waters across the equator, would be greatly increased, and even the coast of Greenland would enjoy a warm and equable climate; and such a temperate climate must once have ruled in Greenland. Professor Heer has concluded from his examination of the fossil flora that the temperature of Greenland was about 30° higher than it is now. You will find from Professor Heer's “Contributions to the Fossil Flora of North Greenland” much wonderfully calculated to revolutionize our notions of the climate of the north of Europe. In the deposits of the outskirting land under the great ice-field which now obliterates all indications of hill and valley were found “thirty different kinds of cone-bearing trees, including species allied to the gigantic Wellingtonia, at present growing in California, with other trees, such as beeches, oaks, planes, poplars, maples, walnuts, limes, a magnolia, hazel, blackthorn, holly, logwood, and hawthorn. These were represented not merely by leaves, which occurred, however, in vast profusion, but by fossil flowers and fruits, including even cones of the magnolia, thus proving,” says a writer in the “ Popular Review,” “that they did not maintain a precarious existence, but ripened their fruits. Vines twined round their trunks—beneath them grew ferns having broad fronds, and with them were mingled several evergreen shrubs.” These deposits belong to the miocene age.
I wish to dwell on this because it has a meaning which must not escape us. In latitudes so high as those of Greenland, no hypothesis, based on an assumed elevation or depression of land, will account for the warm climate which must have existed in Greenland in times remotely ancient. We might look to changes in the great luminary whose rays vivify either directly or indirectly all growth on earth. But additional light is thrown on this subject if we accept Croll's hypothesis. During the glacial period in the south, the medial line of the trades may have been shifted some 20° to the north. Under such a condition of things, says Croll, the warmest part would probably be somewhere about the tropic of the warm hemisphere, and not, as now, at the equator; for since all, or nearly all, the surface water of the equator would then be impelled over to the warmer hemisphere of the north, the tropical regions of that hemisphere would be receiving nearly double their present amount of warm water, and Greenland would enjoy a temperature at least 30° degrees higher than at present. And when the snow accumulated in the southern hemisphere, and attained its maximum, we should have the
glacial epoch of Dr. Haast, with its enormous glaciers creeping into the plains.
The fossil flora of Greenland is the circumstantial evidence of strange physical changes. To my mind it has a romantic interest, and must surely influence us all in our conceptions of the past history of the world we inhabit. Although these discoveries do not point to any wild convulsions of nature, there are other evidences of startling antiquity that certainly prove that stupendous forces were once in activity.
As respects the sun, there must have been in the past, and there will be in the future, great variations in the intensity of the forces in operation. Even in our short lives one summer's heat varies with another, and it may be said with almost absolute assurance that in far off ages of the solar system the heat radiated from the surface of our great luminary may have been less than at present, and, rejecting Croll's theory, you may ascribe the origin of the glacial epoch to a large diminution of the radiant heat of the sun.
The highest manifestation of intellect is that mental progression, which, passing step by step in its accurate review of nature, seeks resemblances, and for what, in the nomenclature of mathematics, is termed “the continuity of phenomena,"—never flying “far and wide” of its mark,—but with unyielding tenacity cautiously seeks in the sun and the planets for the same relation of Things which are found in the globe we inhabit. It seems to me that the first great step made in our knowledge of the sun was that important law which Spencer sought to establish, that the sun matter must conform to the same laws which govern matter here. Nothing can be more interesting than Spencer's remarks on the physical constitution of the sun, and I cannot understand why a higher value has not attached to the profound thought and far-seeing ponderings of this truly capacious intellect. All the credit is given to those who have marvellously verified Spencer's ideas by direct observation with the spectroscope.
It may be well, writes Spencer so far back as the year 1858, to consider what is the probable condition of the sun's surface. Round the globe of incandescent molten substances forming the visible body of the sun there probably exists a stratum of dense aeriform matter made up of sublimed metals and metallic compounds, and above this a stratum of comparatively rare medium analogous to air.
How superior these propositions appear to the fanciful notions of late astronomers, who fluttered around their far-fetched notions, and fancied, because they coined new words, that they were in progress.
The governing idea which animates the present age, the grand field of modern generalization, is the universal acceptance of the law that the same matter, ruled by the same laws, exists within the sun, the stars, and the
world we inhabit; and the grand conception is that the earth, the planets, and the sun, are all under a law of transition. This is the lumen siccum which is diffusing its rays all around—developing the most astonishing revolutions in natural philosophy. Well may men like Tyndall and Spencer rejoice in lofty labours.
The heat on the sun's surface is so intense that the elements of compound bodies are torn apart by its destructive energy. The chemical union between oxygen with iron, magnesium, calcium, etc., is over-mastered. Both gas and sublimed metal rise into the higher regions of the sun's atmosphere; the metals carry with them in their vapourous state enormous supplies of latent heat, absorbed from the molten surface of the sun. In the higher and less heated regions of the sun's photosphere the atoms of oxygen and metals are again brought within the powers of chemical forces, and by their mutual attraction clash together in fixed proportions, forming there the incandescent willow-leaf forms of Nasmyth. These, in their condensed form, dart into space heat, light, and electricity; their latent heat becomes sensible; and they sink again to the surface of the sun, again to gather up fresh stores of heat and light, again to rise up to the upper regions of the sun's photosphere, to be there again subject to the forces of chemical affinity, and in their hot conflict to be the immediate source of radiant heat and light, and so on through countless cycles, radiating into stellar space the sun's almost exhaustless supplies of heat, light, and electricity.
The younger Herschell speaks of these feculæ, or willow-leaf forms, almost with an abuse of the imagination, as amazing organisms partaking of the nature of life, each not less than 1000 miles in length, whose fiery constitution, as Proctor remarks, “enables them to illume, warm, and electrify the whole solar system. Truly Milton's picture of him who in the fires of hell lay floating many a rood, seems tame and commonplace compared with Herschell's conception of these floating monsters.”
These marvellous displays of chemical forces cannot possibly have been equally intense in all ages, and there is a possibility that the glacial epoch was the result of diminished intensity of the forces in operation in the sun.
Next, as to the heat from the body of the earth itself. I have not without a purpose alluded to the astounding fact made known by the spectroscope, that the sun is composed of the same substances as those which form the earth. And I now wish you to admit the probability that those forces which are in activity in the sun were once in a like activity in the planets, our earth, and the moon; and that our earth is in an intermediate stage between that of the sun on the one hand, and the moon on the other. In the moon the chemical forces are exhausted. Every change arising out of chemical com-binations is completed, and with that completion all further display of heat
and light. In the sun, on the other hand, from the greater length of time necessary to complete the cycle of chemical transformation in so enormous an orb of matter, chemical union is momentarily taking place, to be again torn asunder, as revealed to us by his heat and light. It is a barren philosophy which leads us to ignore the forces we daily witness on the globe we inhabit. The grand force in operation around us is chemical affinity—it has wrought all the grand phenomena of nature; everywhere are seen its gigantic structures—the crust of the earth—the waters on its surface—everything we touch—life itself is the creation of this marvellous force. The mild anti-paroxysmatism of Hutton and others is being broken down. Lime, magnesian rocks, clays, etc., which form the crust of the earth, are definite compounds of oxygen with the respective metals, calcium, magnesium, and aluminium. These elements must once have been separate, and their union must have been accompanied by the same enormous display of heat and light, of which we have now an example in the mighty chemical actions in activity in the sun, And there remain unquestionable proofs of past high temperature in the rate at which the temperature increases on descending below the earth's surface.
There is every reason to believe that the condition of things which probably exists in the planet Jupiter was for ages the fixed condition of our globe. Proctor expresses his firm belief that no one can study that planet for many hours without becoming convinced that the cloud masses which envelope his disk have a depth of at least one hundred miles, and he goes on to show that the pressure of such a depth of atmosphere would be so enormous that the lower stratum could not possibly exist in a gaseous state except at an enormously high temperature, and thus we are driven to the conclusion (to use Proctor's words) that “Jupiter is an orb instinct with fiery energy—aglow it may well be with an intense light which is only prevented from manifesting itself by the cloudy envelope which enshrouds it.” The same envelope which prevents the passage of light hinders also the loss of heat from the body of the planet.
These views are strengthened, adds Proctor, by the remarkable phenomenon that for three or four years Jupiter's mid-zone has been aglow with a peculiar ruddy light, but has lately returned to the ordinary creamy white colour. This change of colour was probably owing to some great commotion in the glowing mass beneath making itself manifest by its greater energy through the vast depths of his cloudy envelope.
There must have been a time when the heat of the ocean and of the surface of the earth were retained by a similar deep envelope of clouds, followed by a less heated state of the globe, when plants, of whose profusion and rapid growth we can scarcely form a conception, might have enjoyed the combined heat of the globe and the radiant heat of the sun.