Art. LX.—The Last Glacial Epoch: explained by Major-General Drayson's Discovery of the Second Rotation of the Earth.
[Read before the Wellington-Philosophical Society, 23th June, 1894.]
As you have re-elected me as your President for the present year, the duty once more devolves upon me to open the session by an inaugural address, and I have chosen as my subject one which I hope-may give rise to some interesting and instructive discussion—namely, that slow movement of the north pole of our earth which has long been known in an imperfect manner, but which has now been reduced to mathematical exactness by Major-General Drayson, and discovered by him to be caused by a second rotation with a very long period. The bearing of this discovery upon the date and duration of the last glacial epoch, and the explanation which it affords of that peculiar epoch of the earth's history which immediately preceded man's appearance, are extremely interesting, and I propose to bring the whole matter briefly in review before you this evening.
In speaking of an ice age or a glacial epoch, I do not refer to anything like a cataclysm, but simply to an extension southwards in the Northern Hemisphere and northwards in) the Southern Hemisphere of climatic conditions such as now exist within and near the arctic and antarctic circles. And I assume that this extension of refrigeration was not sudden in its beginning or its ending, but was gradual and slow, and that the effects of such refrigeration were different in different
places, just as we see that there are very great differences now in climate between places in the same latitudes but under different conditions as to heights above the sea, moisture, and the vicinity of cold or warm ocean-currents, & c. With these explanations I may confidently assert that it is a fact, supported by such a mass of geological evidence as to put it beyond the possibility of doubt, that there was a time in this world's history—comparatively recent from a geological point of view—when, climatic conditions somewhat resembling those now existing in Greenland and other arctic and antarctic regions extended very much farther southern the Northern Hemisphere, and also very much farther north in the Southern Hemisphere, than at present. It is, perhaps, not yet quite certain that this glacial condition in the Southern Hemisphere was synchronous with the glacial condition in the Northern Hemisphere, but I believe that the geological evidence is in favour of this conclusion. This remarkable fact in the history of our globe has given rise to much speculation, inquiry, and discussion. The questions to be solved were three: 1. When did this ice age terminate? 2. How long had it lasted? 3. What was the cause which produced it, and why did this cause cease to act? In no part of the world has the ice age left its record so completely and on so grand a scale as in North America. The record has there been studied most carefully and exhaustively; and fortunately there are in that country several cases in which rivers, which, from the circumstances of the case, could not have been flowing during the ice age, have cut back new channels at waterfalls, since the disappearance of the ice, for distances which, when compared with the rate at which the edges of the waterfalls have retrograded during recent times, give a fair measure of the time during which these rivers have acted, and therefore of the date when glacial conditions ceased there. The Niagara Falls is the best known of these instances; but falls on the Missouri at St. Anthony and on other rivers have given similar evidence; and the general result arrived, at is that the glacial condition, both in North America and in Europe, terminated from 10,000 to 8,000, or even less, years ago. The duration of the glacial condition has been estimated approximately by American geologists at from 12,000 to 24,000 years, and by Professor Prestwich at from 15,000 to 25,000 years. These latter are wide margins; but the data, chiefly the masses of moraine left by the retreating ice, and the distances travelled by erratic boulders compared with known rates of glacier motions, are so imperfect that probably no nearer approximation can be made geologically. The theory of two separate ice ages, in succession has been upheld by some; but it is now discredited in America, the appearances which seemed to indicate these
successive waves of cold-having been more carefully interpreted by comparison with existing glaciers, and having been explained by the alternate advances and retirements of glacier faces according as the seasons during the Glacial period were more or less favourable to the deposition of snow or to its melting away.
In North America, the glacial condition extended on the east coast as far south as New York, in lat, 41°; it swept as far south as lat. 38° in the valley of the Mississippi, whence the boundary stretched north-west to about lat. 46° 30′ on the west coast, with great southward extensions on the mountainranges of the Rockies, the Sierra Madre, and the Sierra. Nevada and Cascade Ranges, to lat. 42°, 38°, and 36° N.
In Europe, ice and snow overwhelmed the whole of Ireland, Scotland, Wales, and England as far south as the valley of the Thames in lat. 51° 30′, stretched across to Holland and North Germany, trended south to the Carpathian. Mountains in lat. 48° N., stretched across Russia to the valley of the Volga in an irregular line, a little north of the 50th parallel of north latitude, and thence struck northwards to the Ural Mountains in lat. 63°, and so back to the Arctic Ocean. The Alpine glaciers formed an outlying glacial sea overwhelming Switzerland and North Italy, and invading France by the valley of the Rhone to lat. 46°.
Two remarkable facts are evidenced by these boundaries of the glaciated regions in America and Europe. First, we notice that the Gulf Stream must have had the same sort of influence during the glacial age that it has now; for the glacial conditions on the east coast of North America extended as far south as lat. 41°, while on the west coast of Europe they did not reach farther than lat. 51° 30′. It is probable that this was the limit of the northward flow of the Gulf Stream in the ice age, at least in winter, when the North Sea must have been blocked with ice, and the Arctic Ocean must have formed an icy barrier between Greenland, Iceland, and the British. Isles.
Secondly, we notice how necessary moisture is for the formation of glaciers, as there is no geological evidence of any glacial action in north central Asia; it is confined to the parts of Europe subjected to the moist winds from the Atlantic and the northern seas. In North America the great lake-system was evidently much extended during the ice age, and thus the needed moisture was afforded in the central parts of North. America where glacial conditions prevailed.
In Siberia and Kamschatka and north west Alaska the climate is very dry, and, although the cold is intense, the effect produced is not the formation of glaciers, but what is known as tundra, where the soil is perpetually frozen for hundreds of
feet in depth, a few feet of the surface being thawed in summer and supporting a peculiar vegetation. In such countries the ice age has naturally left no record.
In the Southern Hemisphere the only existing land-surfaces which probably could have been affected by an ice age are Tierra del Fuego and Patagonia at the south extremity of South America, New Zealand and Tasmania, and in some slight degree South Australia. Of the former countries we have no sufficient exploration to give complete geological data on which to reason as to the extent of glaciation they may have undergone in the past; but Darwin found erratic boulders in lat. 41° to 43° on Chiloe Island, evidently brought by glaciers from the Cordilleras, and on the east coast he found similar boulders in Santa Cruz valley, lat. 50°, but he did not examine the country farther north. At present we have the remarkable fact that the mountains on the west coast of South America, as far north as the Gulf of Penas, lat. 46° 52′, send large glaciers down to the sea-coast, where icebergs are formed, and this although the mountains there do not exceed 6,000ft. in height. The degree of cold experienced so far north on this coast is, however, explained by the existence of a cold antarctic current, which, starting apparently to the east of the projecting antarctic land, called South Victoria, circles round to the north and east until it strikes the west coast of Patagonia in lat. 48°, where it divides, part going up the coast northwards until it merges in the west-flowing equatorial current, part flowing south and sweeping round Cape Horn, and continuing onwards in a north-easterly direction into the South Atlantic. This cold antarctic current performs for the south-west of South America a similar but opposite office to that which the warm Gulf Stream performs for the north-west of Europe, and, just as the Gulf Stream gives north-western Europe an abnormally high temperature, so this antarctic cold stream gives an abnormally low temperature to the south-western coast of South America. The south-east coast has a much more genial climate. And here I would protest against the statement so often made that the Southern Hemisphere is colder than the Northern Hemisphere. Darwin probably gave rise to the idea by comparing south-west South America with north-western Europe, which is warmed by the Gulf Stream. North-eastern North America almost exactly corresponds in. climate with south-western South America. Newfoundland, in the same north latitude as Penas has south latitude, has a very similar climate, being also chilled by an arctic current, although. it has no high mountains as nurseries for glaciers. Comparison is, however, very difficult on account of the very different distribution of land and water in the two hemispheres. If we take the corresponding north and south latitudes of 42°
we find in the best physical atlas that the mean temperature in the depth of winter in the Northern Hemisphere varies in different places between—4° and +41°, while in the Southern Hemisphere it is about +45°. In the height of summer in the Northern Hemisphere in this latitude the temperature varies in different places between 54° and 77°, while in the Southern Hemisphere it varies very little from 59°; or, if we take the mean for the year, in the same latitude north it is 52°, and south it is 55°. As we might expect, in the Northern Hemisphere, with its great continents, the range of temperature is very great; while in the Southern Hemisphere, with but little land and vast stretches of ocean, the temperature is more equable, but at the same time it is somewhat higher on the average, and this notwithstanding the present position of the equinoctial line in the earth's orbit, which causes the summer to be shorter and the winter longer in the Southern Hemisphere than in the Northern by a few days.
The effect of cold and warm ocean-currents is well exemplified in the Northern Hemisphere by the line indicating the extreme north limit where cereals will ripen. On the east coast of North America, chilled by the arctic current, the limit is lat. 48° N.; while in north-west Europe, warmed by the Gulf Stream, the limit extends to the North. Cape in lat. 72° N. On the west coast of North America, which is not chilled by an arctic current as the current flows into Behring Straits, the limit of cereals is about 58° 30′. We have no land in similar positions in the Southern Hemisphere to compare with these except in New Zealand; Stewart Island, lat. 47° S.; and Tierra del Fuego, lat. 53° S.
As regards the geological record of glacial action on an extended scale in New Zealand in geologically recent times, it is plain and abundant in the Provinces of Otago and Canterbury, and, as I am informed by Mr. McKay, as far north as the Grey River Valley on the West Coast in about lat. 42° 30′. As to the limits of glacial action on the east coast of the Middle Island, and on the question of any means we may have of judging either the duration or the date of the termination of this epoch in New Zealand, I will say nothing; but I hope we may have some valuable information on these points from Sir James Hector, Mr. McKay, and others who are experts in the geology of New Zealand.
It has occurred to me, however, as being highly probable that the peculiar surface-carving of the clay hills around Wellington may be traced to the climatic conditions of the Glacial period, when there must have been very severe winter frosts here, with heavy snowfall, and very hot summers, producing rapid thawing and violent torrents of water stream-
ing down the hillsides, and cutting out the very prominent gullies which are so characteristic of the view which we see every day as we look across the harbour, or observe the hills enclosing Wellington. That the frame work of this rugged country was due to other and preceding causes there can be no doubt; but that the surface-cutting must have been the result of the erosive action of water in a much more violent form than is experienced in our existing climate seems equally certain, and I think that, although the climate in this latitude was not so severe as to allow of the formation of glaciers at the time when they were so marked a feature in the southern parts of the Middle Island, yet the winters must have been so severe as to insure a heavy snowfall throughout the long ages of the Glacial period, which has left its mark in this way by the water erosion of melting snow and heavy rains, although not by the grinding action of the consolidated snow in glaciers.
In Tasmania, evidences of extensive glaciers in former times are now found in about lat. 42° S., or nearly the same latitude as the northern limit in New Zealand. A very interesting paper on the subject, read before the Royal Society of Victoria by Mr. E. J. Dunn last year, has been kindly put into my hands by Sir James Hector. Mr. Dunn describes the district he visited near Zeehan, in the western highlands of Tasmania, which do not exceed in altitude from 1,800ft. to 3,800ft., and where the records of glaciers are left in moraines, erratic blocks, and the characteristic planing, scoring, and polishing of rocks. He observes that in the higher mountains farther south and east he is confifident that still more extensive records of the last ice age will be found. He says that the appearances indicate a comparatively recent date for the glaciers which must have formerly existed in the neighbourhood which he visited.
In a paper read before the Royal Geographical Society in March, 1893, by Mr. H. O. Forbes, which has also been shown to me by Sir James Hector, Mr. Forbes refers to evidences of glaciation in South Africa as far north as lat. 27° and 30° S. I should imagine that these evidences are either on very high mountains, or that they belong to an earlier geological date than those in other parts of the Southern Hemisphere, which are not found farther north than lat. 36° S. He also refers to evidences of glacier-action in South Australia in lat. 36° S. I presume that he alludes to the ice records in St. Vincent's Gulf, near Adelaide.
Mr. R. M. Johnston, F.L.S., in a very exhaustive paper read in June last before the Royal Society of Tasmania and also furnished to me by Sir James Hector, explains these markings and erratic blocks by the stranding of icebergs on the
shore during a period of refrigeration, and by the subsequent raising of the shore to its present height of 40ft. above sealevel. This seems to be a reasonable explanation of the record of ice-action on a low shore in lat. 36° S. In this paper Mr. Johnston gives a mass of very interesting and valuable information relative to glacier-action amongst the Australian Alps in lat. 36° 30′ S. Mount Kosciusko and its neighbours, over 7,000ft. high, show evidences of former glaciers, but at high levels only. This corresponds with similar evidence in Colorado and New Mexico, in North America, where the mountains are 14,000ft. high, and formerly had extensive glaciers, reaching to about the 5,000ft. level.
In Tasmania he gives additional facts corresponding with those mentioned in Mr. Dunn's paper, showing that in recent geological times there were extensive glaciers in the western highlands of Tasmania, where the mountains are from 4,000ft, to 5,000ft. high; but there is no evidence that they reached the sea, although they have left their marks in the river-beds and on the low-lying land.
Mr. Johnston is disposed to assign a more remote antiquity to these indications than is Mr. Dunn, but Mr. Johnston is evidently influenced by the astronomical theory of Dr. Groil, and it does not appear to me that he brings any evidence to support this view, which would refer the indications of glacieraction in Australia and Tasmania, where no glaciers now exist, to 80,000 or 100,000 years ago, instead of 8,000 or 10,000 years ago as in the Northern Hemisphere.
If we inquire what were the circumstances of those parts of the earth which were affected by it during the ice age, we find these circumstances must have been very various. The most common evidences of ice-action are moraines, or the collection of boulders and stony material confusedly piled together, and often scratched and polished; erratic blocks far removed from their parent rocks; grooyings, planings, and roundings-off and polishing of rocks in situ; in some places deep beds of tough clay mixed with scratched and rubbed stones, known as “till,” in others “kettleholes” or deep hollows in the ground; long lines of deposited stones and other material, like the beds of streams, only raised in relief above the surrounding surface; and many such strange, evidences of a mighty power at work, quite different from the ordinary work done by rains, and streams, and rivers, and seas, or by volcanic agency. In many instances the work has evidently been done by glaciers, as it is precisely similar to that now being carried on by existing glaciers; but where such evidences are found at a great distance from mountains—on the plains of America, Canada, central Europe, and in England—we are constrained to seek for some agency different
from ordinary glacier-action. Some geologists, who have studied the existing conditions in Greenland, believe that during the ice age a great covering of snow and ice, thousands of feet in thickness, overwhelmed wide districts in the regions, where these evidences exist, and that by its agency nearly all these effects were produced in America as it accumulated and advanced, or diminished and retired. The geologists of the United States Geological Survey hold this view, and it is most ably set forth in Dr. Wright's most interesting and comprehensive book.
The Canadian geologists, with Sir William Dawson at their head, consider that there was a great submergence of the low land in the glaciated regions of North America and Canada during the ice age, and that a great part of the deposits were made by icebergs and shore-ice during this condition of things.
It seems probable that, as in most such controversies, and as, indeed, Sir William Dawson holds, both sides are partly right, and that submergence of the land and the inroad of cold currents carrying icebergs and depositing their burdens of stones and earth on the sea-bottoms, and compressing and ploughing the shores as they stranded, will account for many of the effects noticed; but they certainly will not account for all of them, and in many large districts great thicknesses of snow and ice, carrying boulders and stones and earth and other things, must have covered the hills and valleys, in the same way as Greenland is covered now, creeping outwards from the highest snow-covered land to immense distances.,
In many places there is no evidence of any extensive glaciation of low lands, but only of the existence of glaciers of greater or less extent on mountain-ranges, and extending down the valleys from them, where no such glaciers now exist. Such seems to have been the case in Tasmania, and, I believe, in New Zealand; but, whatever the special results in each locality, they all alike indicate a more arctic climate where they occurred than now exists there.
The third question still demands an answer, What was the cause which produced the last ice age, and why did it cease to act?
Some geologists, and eminently Sir William Dawson, the Canadian professor, have suggested that an efficient cause may be found in those elevations and depressions of land which are well-known geological facts, and which doubtless may have had considerable climatic influence.
Sir William Dawson thinks that there is reason to suppose that during the last ice age in North America the Isthmus of Panama was submerged, and thus the Gulf Stream was not thrown northwards as at present; and also that a consider-
able part of North-America was submerged; and he conceives that the greater extent of sea and the absence of the warming influence of the Gulf Stream would account for the change of climate. We have seen, however, that there is the strongest ground for believing that the warm Gulf Stream exercised the same influence on the north-western shores of Europe in the ice age as it does now; and the conditions of the Southern Hemisphere are at the present time even more favourable for the production of an ice age than those he conceives to have existed in North America during the Glacial period in regard to the distribution of land and water, yet we certainly have no approach to an ice age in the Southern Hemisphere now. We may therefore conclude, I think, that no redistribution of land, and water can have been the main factor in the phenomenon.
The question, then, naturally arises, Can there have been any astronomical causes which would suffice to explain the occurrence of an ice age terminating from 7,000 to 10,000 years ago after having endured for from 12,000 to 25,000 years? Dr. Croll has attempted to give an astronomical reason, and Sir Robert Ball has lately perfected his suggestion.
I will not attempt to explain the astronomical theory as put forward by Sir Robert Ball in his most charming and interesting little book, “The Cause of an Ice Age,” but merely give his conclusions, which are as follow: He shows, first, that, with, the present obliquity, or approximately the same, “of the total amount of heat received from the sun on a hemisphere of the earth in the course of a year, 63 per cent, is received during the summer and 37 per cent, is received during the winter.” He then goes on to show that the ellipticity of the earth's orbit round the sun varies within certain limits by disturbances caused by the other planets, and that at certain extremely long intervals this ellipticity attains its maximum. This maximum endures for a very long period, and then gradually diminishes to its minimum again. He also shows that, owing to the precession of the equinoxes, combined with a very slow motion of the major axis of the earth's orbit in an opposite direction, the line of equinoxes travels all round the ellipse in about 21,000 years. This period appears to be incorrect, and should be about 32,000 years, but in any case it is a short period compared with that occupied by the change in the ellipticity of the orbit, so that the line, of equinoxes may travel round several times during a period of high eccentricity. He then explains that when “during this period of high eccentricity of the orbit the line of equinoxes cuts the major axis at right angles, one hemisphere will have a very long summer (199 days) and a very short winter (166 days), while the other hemisphere will have a very short summer (166 days) and a very long winter
(199 days); yet in both cases (supposing the obliquity to remain constant) the same inequality will exist in the total amounts of heat received during summer and winter in both hemispheres—i.e., 63 parts in summer and 37 parts in winter. Hence the hemisphere which was enjoying a long summer would have its heat tempered by the length of time over which it was distributed, and its short winter would have a fair amount of heat each day; but the other hemisphere would have only the same amount of heat distributed over all the days in its long winter, while its short summer would be intensely hot. Such conditions, he considers, and shows mathematically, would be very different from those now experienced on earth, and might well produce long periods of genial or arctic climate on one hemisphere and then on the other. The alternations in climate between one hemisphere arid the other would, he states, each have a period of 10,500 years from commencement to end, a complete cycle lasting 21,000 years, and these cycles would probably be recurrent two or three times or more during each period of extreme eccentricity.
Dr. Croll gives the dates of these periods. The latest culminated 200,000 years ago, and ended 80,000 years ago; another culminated 750,000, another 850,000, another 250,000 years ago; and the next will occur 500,000 years hence.
Now, if we accept the geological inferences from the known facts of the last ice age in the Northern Hemisphere,—and they are so convincing that we cannot refuse our assent,—it is clear that the cause of that ice age was not the eccentricity of the earth's orbit combined with a favourable position of the line of equinoxes, whatever effect may have been produced by such a conjunction in past ages.
I will now pass on to put before you the view of Major-General Drayson, an artillery officer who has devoted the greater part of his life to the study of astronomy, and who has made a discovery which, although it has not yet met with universal recognition, is steadily making its way into the position of a fundamental astronomical fact. The discovery is this: that our earth is not only revolving daily on an imaginary axis at present inclined 23° 27′ 22–3″ to the plane of the ecliptic, or its orbit round the sun; but that it is also slowly revolving in nearly the opposite direction on another imaginary axis, the pole of which is 6° from that of the ecliptic, 29° 25′ 47″ from the pole of daily rotation, and has a right ascension of 270°, or 18 hours (Plate XLV., fig. 3). The discovery of this second rotation of the earth is fraught with most important consequences. It explains most simply the cause of the precession of the equinoxes and the varying obliquity of the ecliptic, and defines the rate of precession and the amount of the obliquity
at any date; it fixes the apparent motion of the north pole of the axis of daily rotation with accuracy, and also the corresponding motion of the south pole; it explains and enables us to calculate easily and certainly the true apparent position of every star hundreds of years ago and hundreds of years hence; and it shows us that, under the present conditions of the globe, the period required for a complete second rotation is 31,686 years (Plate XLV., fig. 4), and that euring this period the obliquity of the axis of daily rotation to the axis of the plane of the ecliptic would have attained a maximum of 35° 25′ 47″ in the year 13,544 B.C., The obliquity would have been about 30° in the year 21,460 B.C., and would have returned to 30° again in 5,624 B.C. Between those dates—that is, for 15,866 years—glacial conditions, more or less accentuated, would have prevailed in both hemispheres: that is, the arctic and antarctic circles would have been brought from 12° to 6° nearer to the equator than at present, the tropical zone having been, also proportionately widened, and thus much greater extremes of temperature would have been experienced, especially in what are now temperate zones. What the precise results of this great increase in the obliquity of the ecliptic would be no one probably would have been able to predict; but that such a great change in that element of the earth's position, with reference to its orbit round the sun, on which our climatic conditions mainly depend, would accomplish immense alterations in existing conditions no one can doubt. An incident recounted in General Drayson's book is so suggestive N that it is worth reproducing here. He says, “Some years ago, when standing on the banks of a lake in Nova Scotia (a locality well suited to the study of the evidence of the Glacial period), I observed that the hard rocky shore was cut and marked by the glaciers and icebergs of the boulder period. In various inland localities were enormous boulders, which had been carried many miles from the parent rocks, and deposited in what was now a vast forest. My only companion was Paul, a Micmac Indian. Pointing to the boulders and the marks on the rocks I said, ‘Paul, how do you account for all this?’ Paul, without any hesitation, replied, ‘Long time ago more winter in winter, more summer in summer. More winter make more snow, more icebergs; more summer melt snow quicker, float-icebergs more than now. That what I think.’” I have no doubt that the Indian, a careful observer of the natural effects and their causes in the climatic conditions in which he lived, was right in his conclusion. There was more winter, but there was also more summer, and, as Professor Tyndall states, heat is as necessary as cold to produce glaciers and to develope their full effects. Sir Robert Ball has calculated that, with the present obliquity of the ecliptic, each hemisphere of our globes, jreceives
during summer 62.7 per cent, and in winter 37.3 per cent, of the total heat given to that hemisphere by the sun in the year. Calculating by the same method, I find that when the obliquity is 35° the proportions are 66.5 (or two-thirds) in summer, and 33.5 (or one-third) in winter. Such an inequality would produce an exceedingly severe climate.
The period of a complete second rotation of the earth being approximately 32,000 years, and the date of the maximum obliquity of the earth's axis of daily rotation to the plane of the ecliptic being approximately 14,000 years B.C., the termination of abnormal climatic conditions occurred about 5,600 B.C., or nearly 7,500 years ago, and those conditions had endured about 16,000 years. These numbers agree with those separately and on totally distinct grounds assigned by geologists to the duration and termination of the last glacial age. It is to be noted also that General Drayson's calculations were published very many years before geologists had arrived at any distinct and comparatively unanimous opinions on the subject. Astronomically, also, General Drayson's discovery, in his mathematical deductions from it, agrees absolutely with the observations of astronomers in the past two thousand years as to the obliquity of the ecliptic, the precession of the equinoxes, and the positions then occupied by all the principal stars, and this is the best possible proof of the truth of his discovery and the soundness of his reasoning.
The steps which led to General Drayson's discovery of the second rotation of the earth—with all its far-reaching consequences—were somewhat as follow: First, he was puzzled and dissatisfied by the vague and contradictory statements made in all books on-astronomy relative to a conical movement of the earth's axis without fixing the point about which it turned or the centre of the circle it described, about the precession of the equinoxes, and the variations in the obliquity of the ecliptic. He saw that it was geometrically impossible that the pole of the heavens, or the axis of the earth's daily rotation produced to the heavens, should be describing a circle round the pole of the ecliptic as a centre if this latter pole was movable, as was stated; for, if the ecliptic or plane of path of the earth round the sun was variable, the pole of this orbit must be moving also. Besides, it was not stated whether the north pole only was moving, or if the south pole was moving also, which was a very important consideration. Then it occurred to him, Why should the plane in which the earth's orbit lies be movable? Is it not much more probable that the inclination of the earth's axis of daily rotation moves? And the fact that the inclinations of the axes of rotation of the other planets vary from being nearly perpendicular to the plane of the orbit, as in the case of Jupiter, to being nearly
parallel in the case of Saturn, encouraged this idea. La Place and others had calculated that the plane of the earth's orbit could not vary more than a certain small amount,—in which they did not all agree;—but no one had discovered how much ib did move, or where the pole of the ecliptic would be at any particular epoch. Nor had any one attempted to determine what effect the known movement of the zenith of the north, pole of the earth has upon the zeniths of other places on the earth.
As an artillery officer he had studied the gyroscope with reference to the peculiar movements of the spinning projectiles thrown by rifled ordnance, and he knew that a rotating body, if perfectly balanced, maintained the direction of its axis perfectly in the same direction; but he also knew that a very small deviation of the centre of gravity from the centre of form produced a slow second rotation by which the direction of the axis of primary rotation was gradually altered. The question then arose in his mind, Is this what the earth, is doing? Is it also slowly rotating on some other axis, so that the poles of the axis of primary rotation are each describing circles round the poles of this secondary axis? If so, the first point was to find the pole of this axis of secondary rotation. The data he had to work from were the recorded positions of a number of the principal stars, and also the position amongst the stars of the north pole at certain dates extending back for some 2,000 years—from the star catalogue of Hipparchus, dated 140 B.C., and that of Ulugh Beigh, dated 1463 A.D., down to the more complete and accurate lists of later years. He laid down the arc described by the pole of the heavens between those dates, P1 P2 P3 (Plate XLV., fig. 1), and then by careful examination of the star lists he found that a certain star r had not varied its distance from the pole when the pole was at or near P1, while other stars had varied their distances; he concluded that r, was therefore in the direction of the centre of the circle of which P1 P2 P3 was an arc when the pole was at P1, Similarly, when the pole had reached P2 and P8 successively, he found that certain stars s and t respectively did not vary their distances from P2 and P8. The intersections of the lines P1r, P2s, P3t, produced in the point C, showed that C was the centre, round which the pole of the northern heavens was slowly moving in a circle, and this was not the pole of the ecliptic, but 6° from it. Thus he obtained a sure standing-ground, and he proceeded to develope the full consequences of this brilliant and important discovery.
But first he cheeked his conclusion as to the true centre of the circle described by the north pole of daily rotation by means of the geometrical truth that all angles in the same
segment of a circle are equal to one another. He described the circle from the centre found as above, and saw that it passed through several well-known stars (Plate XLV., fig. 2).
Let a and b represent two such stars; P1, P2, P3, successive positions of the pole of daily rotation at intervals of, say, 1,000 years. If, then, Pa b be the true circle described by the pole the angles aP1b, a P2b, must be equal to one another, but if the stars a and b are not in the circumference of the true circle the angles will not be equal. We are not told how many trials were made, and errors found and corrected; but at length the true centre was accurately determined, and it was found to be in the position above stated. It followed, therefore, that each of the poles of daily rotation was slowly tracing a circle in the heavens round the axis of second rotation. The time occupied in describing this arc of the circle fixed the time required for a complete second rotation, and the diameter of the circle passing through the pole of the elliptic gave the dates of the maximum and minimum obliquity and their amounts.
I will not attempt to indicate the astronomical consequences, beyond observing that they reduce to geometric and mathematical certainty what was before vague, and only defined as a conical motion of the earth's axis; the precession of the equinoxes and the obliquity of the ecliptic, which vary in their rates and amounts continually, are determined with perfect precision hundreds of years in advance; so also are the positions of stars for each zenith, for, as he shows, the zenith of each observatory moves by the second rotation in a special direction and at a special rate; and it is proved that in many cases, though probably not in all, the supposed proper motions of the stars are a result of the proper motions of the zeniths of the observatories, caused by the second rotation of the earth, and that the speculations about our system rushing through space towards the constellation Hercules have a doubtful foundation in facts. As General Drayson well puts it, however accurate and powerful our telescopes and observing-instruments may be, the real instrument with which we make our astronomical observations is the earth itself, which by its motions gives us our only means of measurement, and until we know precisely what its motions are we cannot make any really accurate observations.
Enough has been said on the astronomical aspect of the discovery. From our present point of view it is chiefly important from the fact that the most rigid scrutiny has hitherto failed to detect a flaw in the process of reasoning which has led to the discovery of the earth's second rotation, and the geometrical consequences of the discovery have been proved to correspond exactly with recorded astronomical observations
in such a multitude of stars and for so long a period that it is difficult to understand how more general recognition has not been given to the discovery. I fear that there is some human, feeling in the case. Unfortunately, General Drayson appears to have been somewhat embittered by this want of recognition, and in his book he devotes a good deal of space to poking sarcastic fun at the astronomers. They probably feel towards him much as the French engineers did towards the cavalry officer Montalembert, who dared to differ from the great Vauban and the teachings of the French professors of fortification, and to propose a system of his own. It was scouted and considered as rank heresy for many years; but he was right, outsider though he was, and their orthodox systems have disappeared from the modern civilized world, and have been replaced by the ideas of the cavalry officer. So, I venture to believe, will the second rotation of the earth, with all its far-reaching consequences, be universally accepted as true doctrine before many years are passed. Already the Royal Astronomical Society have tardily taken the first step by conferring the fellowship of the society on General Drayson.
With regard, however, to the geological aspect of this second rotation, it is objected that it saddles us with a succession of glacial ages at regular intervals in the past, of which we have no evidence: indeed, we have evidence of a genial climate in arctic, regions immediately preceding the glacial climate, and in former periods of the world's history we have evidence of climates very equable all over the earth at certain times.
General Drayson suggests, to meet this difficulty, that similar cause to that which probably produced the existing second rotation on an axis in its present position may under different conditions have produced a second rotation round a different axis, and, as a consequence, very different climatic conditions.
We know that at different periods in the world's history there have been very different distributions of sea and land from those which now exist. Now we have the bulk of the land in one part of the Northern Hemisphere. Supposing this special distribution to be the cause of the existing second rotation—as it well may be, small as the mass of the land above water is compared with the mass of the whole earth, for it alters the symmetry of the globe, and throws the centre of gravity some small distance out of the centre of the axis of daily rotation, and any such difference must inevitably cause a second rotation—admitting this cause, then, we can see that any considerable submergence of land in one place and elevation in another would alter the position of the centre of
gravity, and set up a secondary rotation on some other axis. We may suppose, for instance, that previous to the Glacial age the axis of second, rotation was in some such position as C1 (Plate XLV., fig. 5), under which conditions the pole of daily rotation would have been close to E, the pole of the ecliptic, for many thousands of years, and consequently a uniform climate, without changes from summer to winter, would have prevailed all over the globe, although of course it would have been hotter near the equator than near the poles. If, when the pole reached A at the culmination of the Glacial period, the distribution of land and water were altered to approximately what it is now, so that the pole of the axis of the second rotation were shifted to C, the movement of the pole of daily rotation would gradually diverge from the path of the smaller circle to that of the larger, which it now pursues. This suggestion of General Drayson's is merely a hypothesis, which possibly might account for the more genial climate in arctic regions which geological evidence shows, to have existed previous to the Glacial age. The hypothesis would involve a shortening of the period of extreme cold by three or four thousand years. But when once we recognize the fact that any alteration in the form of the surface of the globe which moves the centre of gravity from its symmetrical position must cause a second rotation about an axis depending upon the balance of the globe at the time, we have a wide field of investigation opened to us as to the possible changes of climate which may have occurred during the past history of the globe.
In order to show that this cause of a second rotation of our globe is reasonable, we may make a rough comparison between the present conditions of the earth and those experimentally produced with a gyroscope.
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The most recent estimates of the extent of land in the Northern and Southern Hemispheres at present give an excess in the former of about 23,000,000 square miles, the greater part of it lying in the eastern part of the hemisphere. Assuming 1/10th of a mile, or about 500ft., as the average height of the land above the water, this would give 2,500,000 cubic miles of land. The volume of the globe is 260,000,000,000 cubic miles, and its density as a whole is about twice that of the upper strata: hence we find that about 1/226087th or, say, 1/230000th part of the mass of the earth projects at one point and throws it out of equipoise. Is this a sufficient cause to produce one second revolution in about 32,000 years, equivalent to 32,000 × 365 = 11,680,000 daily revolutions?
I assume the weight of a wheel of a gyroscope to be 11b., and that it is revolving fifty times in a second, and make a comparative rule-of-three statement to find how many of these
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revolutions would be required to produce a second rotation if a weight of ½oz., or 1/32nd part of the weight of the wheel, were added to one side to throw it out of balance, as compared with the 1/230000th of the mass of the earth which destroys its balance and produces a second rotation in 11,680,000 revolutions of weight of gyroscope: 1/230000 of weight of earth:: 11,680,000 revolutions of earth = 1,625 revolutions of the gyroscope, or 32 seconds. That is, under the above conditions the gyroscope ought to complete a second rotation in a little oveir half a minute; and this is approximately what would happen. Of course the comparison is very rough, because friction interferes very greatly with the action of the gyroscope, and the mode of the attachment of the extra weight and the direction of the pull of gravity are different; the estimate also of the protuberance on the earth is very inexact: still, it is sufficient to show that the second rotation of the earth is not only a fact discovered and proved astronomically, but that an efncien't cause to produce this effect exists in the present distribution, of land and water on the earth: Possibly the inequality of the earth's equatorial and polar diameters (to which Herschel in his popular explanation attributed the precession of the equinoxes) may have a perturbing effect, as the inclination of the earth's axis of daily rotation to the plane of its orbit varies in its second rotation.
There is, as I have said before, a wide field for future investigation opened up by this discovery of the second rotation of the earth, and most, probably it will be found that some minor corrections must be made in some of General Drayson's results, owing to perturbations resulting from other causes. But the beauty and simplicity of the secondary motion of the earth which has been brought to light by his sagacity and lifelong persistent labours seem to me to rank with the highest discoveries of astronomy, and the name of Drayson will in the future stand very high in the list of the great astronomers,*
In connection with the ice age the historical nature of General Drayson's discovery is of deep importance, and, whether the great increase of the inclination of the earth's
[Footnote] * This discovery will no doubt produce a revolution in astronomical observatories, as the laborious observations now made year by year to ascertain the apparent motions of the stars, and so by empirical rules to calculate their apparent positions a few years in advance for the compilation of the “Nautical Almanac,” have become useless. The apparent movement of each star, caused in reality by the second rotation of the earth, can now be calculated with perfect accuracy for hundreds of years in advance. A few competent men with calculating-machines can easily perform what has hitherto needed a great staff of observers with astronomical instruments and subsequent laborious reductions of their observations. Astronomical time, also, which has hitherto needed to be fudged from time to time, will now be accurately determined.
axis of daily rotation to the plane of its orbit, which he proves to have occurred in both hemispheres for some 16,000 years, ending about 6,000 years ago, was or was not the sole efficient cause of the glacial conditions which immediately preceded the present climatic state of the earth in the Northern Hemisphere, it must have been a most important factor. Should it appear that glacial conditions were synchronous in both hemispheres, the astronomical explanation would seem to be complete.
This is really a crucial question, and I hope we may have some light thrown upon it this evening, as I suppose there are no living authorities so competent to give an opinion on the subject as some of those now present. My own imperfect observations, which have, been confined to the valley of the Waitaki and to the vicinity of Lake Wakatipu, have led me to believe that the great moraines and other evidences of glaciation to be seen there are geologically very recent: indeed, owing to the slight changes made by the hand of man in this country, they have the appearance of being even more recent than similar evidences of old glacial action which I have seen in Europe, because the latter have been considerably modified in most cases by human agency. If there be no strong reasons which would lead a geologist to assign a date for the southern glaciation some 100,000 years prior to that of the glaciation in the Northern Hemisphere, the astronomical changes traced out by Sir R. Ball cannot have been effective in this matter. Indeed, his explanation throws the whole cycle of changes 80,000 to 200,000 years back, which is contrary to geological evidence in the Northern Hemisphere, with which, however, Drayson's discovery, with its consequences, is perfectly in harmony.
Should it be established on sound geological evidence that the last ice age in the Southern Hemisphere was synchronous with that in the Northern Hemisphere, the harmony between geological results and astronomical causes, as demonstrated. by General Drayson, will be complete for the last ice age. Prestwich states that he has been unable to obtain any reliable evidence of glacial action in any of the formations between the Permian and the Recent; other geologists have thought they had evidence of intermediate ice ages. Possibly Sir R. Ball's theory may throw light on this question; but, as regards the last ice age, no cause that has been suggested appears to have weight or fitness compared with that resulting from General Drayson's discovery of the second rotation of the earth.
I think it was Galileo who, when objections were urged against his statement that the earth was daily revolving—not the heavens—contented himself with remarking, “E pur si muove,” Nevertheless it does move. General Drayson may
well adopt the expression as regards the second rotation of the earth.
To sum up. It has been established by unassailable evidence that the slow movement of the prolongation of the earth's axis of daily rotation in the northern heavens, which has long been known, is the result of a slow second rotation of the earth on an axis the poles of which are 6° distant from the poles of the ecliptic, and having a right ascension of 18 hours; that this slow second rotation is the cause also of the precession of the equinoxes and the varying obliquity of the ecliptic; that this obliquity would have attained gradually to its maximum of 35° 25′ 47″ about 15,448 years ago, and then gradually declined again until the present time. About 7,524 years ago, or 5626 B.C., the period of extreme obliquity would have expired, after having endured for about 16,000 years. During that period the arctic and antarctic circles would have approached the equator from 12° to 6° nearer than at present, and consequently climatic condir tions would have been greatly changed, especially in the zones south and north of the present arctic and antarctic circles. The tropical regions would also have been similarly extended. All this follows if we admit that the earth has been rotating on its second axis during this period of the past as it is now. The geological records of the Northern Hemisphere show that during this period there was an ice age in the above-mentioned zone extending farther south and being more intense in its action in some places than in others, for reasons which we can in a great measure discern. This ice age, then, we must infer was the result of the increased obliquity mamly.
In the Southern Hemisphere there are similar recprds of an ice age, modified by local circumstances as in the Northern. Hemisphere. This ice age is also comparatively recent, and its limits correspond with those in the Northern Hemisphere. We are naturally led to suppose that its cause was the same as that in the Northern Hemisphere, and that it occurred at the same time. It remains for geologists to say, after full investigation and consideration, whether there are any reasons which are insuperable, and which oblige us to disbelieve that the great increase in the obliquity of the earth's axis which occurred in both hemispheres at this time, produced, the effects here which are comparable with those in the Northern Hemisphere.
In consequence of what was said in the short discussion which I invited at the close of my address, I would add that, although the astronomical facts which follow from the dis-
covery of the second rotation of the earth, as to the increase of the obliquity of the earth's axis of daily rotation to the plane of the ecliptic during a period of some 16,000 years, terminating about 7,500 years ago, are in perfect accord with the geological facts in the Northern Hemisphere, yet in the Southern Hemisphere the accord is not yet so well established. The southern extremity of South America is the only land in this hemisphere in which, on account of its latitude south, we could expect to find very marked evidence of the Glacial epoch, and such imperfect acquaintance as we have with this littleknown part of the world leads us to believe that in recent geological times glaciers on a large scale existed in latitudes much farther north than they are now to be found. Tasmania, in its western highlands, gives similar evidence, and even in southern Australia there are some concurrent records of lower temperature in winter than at present. In New Zealand, however, the record appears to be different, and Sir James Hector considers that any evidences of former glacial action should be referred to a much more distant date. The geology of New Zealand is very peculiar: the great faults and dislocations of strata show that in comparatively recent times great changes in level have occurred, and consequently the records of a changed climate during the ice age are very difficult to unravel; mountains which show evidences of glacial action are now at a lower level than neighbouring mountains which show no such evidences. The great sounds on the south-west coast of the Middle Island, if cut out by glaciers, would seem to require a very much longer time than 16,000 years for their excavation. We cannot therefore, at present, draw-any geological support for the second rotation of the earth from New Zealand, beyond the fact that in recent times there were glaciers here where there are none now. Possibly the climatic changes due to the changes in the ellipticity of the earth's orbit ascertained by Dr. Croll and Sir Robert Ball have here left their mark. I will not pretend to be able to decipher what our most able geologists are in doubt about, and must therefore leave New Zealand outside my argument, as an exceptional and perplexing problem; but I must, nevertheless, maintain that the surface of the rest of the earth, within the limits of the extension of the arctic and antarctic regions caused by the second rotation of the earth, has undoubted records of that extension both in the Northern and Southern Hemispheres, and that in Patagonia, Tasmania, and South Australia there is no real reason for supposing that these records were not of the same date as those in the Northern Hemisphere. It seems to me that, when this is established, it will give in the Southern Hemisphere a sure point of departure in time by which we may synchronize the southern
geological epochs with those in the Northern Hemisphere, at least for some distance backwards from the date of the ice age. I need not perhaps refer to other objections raised on the grounds of discoveries in Egypt which are considered to indicate a high civilization there at a very remote date, because the ice age had little or no influence on Egypt or any tropical or subtropical countries. As far as the facts of the ice age are concerned, man may have lived for millions of years in those regions of the globe while north and south the climate would have been very unfavourable for human occupation.
It is, undoubtedly, very remarkable that none of the great astronomers of the past should have discovered, and that few of those of the present day should yet have admitted the truth of, the second rotation of the earth; but this is not the first time in the world's history that such a thing has happened. New truths are slowly accepted, especially when they are opposed to received theories which have the sanction of great names; but magna est veritas et prcevalebit. If General Drayson's discovery be a truth, as I conceive he has proved it to be, it must be accepted in course of time.
Since this address was written and delivered, I have had the advantage of reading “General Astronomy,” by Professor Young, of New Jersey College, in which he explains very clearly the procession of the equinoxes on the principle of the gyroscope.
He shows (pp. 134, 135) that the attractions of the sun and moon on the parts of the equatorial protuberance of the earth which are nearer to them produce a “couple” which is equivalent to a pull on the poles of the axis of daily rotation, tending to bring the plane of the earth's equator into coincidence with the plane of the ecliptic, and that this pull, like that of a weight attached to one end of the axis of a gyroscope, results in the same effect—viz., a slow secondary rotation of the earth in the opposite direction to the diurnal rotation. He assumes, however, according to the received theory, that this second rotation is about the axis of the plane of the ecliptic. General Drayson has shown that, as a matter of fact, the second rotation is about a different axis, and he suggests that the cause is the preponderance of the Northern Hemisphere over the Southern, due to the vastly greater extent of land in the former.
On reconsidering the question in the light of Professor Young's demonstration, I see that the equatorial protuberance is largely, if not mainly, the cause of a precession of the
equinoxes. I also see that the preponderance of the Northern Hemisphere affects the question in a somewhat different way from that suggested by Major-General Drayson, and which in my address I accepted. During summer in the Northern Hemisphere the pull on the equatorial protuberance tending to bring the plane of the equator into coincidence with that of the ecliptic will be directly opposed by the extra pull on the Northern Hemisphere. During winter it will be aided, but in a lesser degree, the north pole being turned away from the sun instead of towards it. During autumn and spring the effect produced by the equatorial protuberance is reduced, becoming zero at the equinoxes. The tendency produced by the northern preponderance will be to draw the north pole towards the sun—i.e., towards the north during autumn, towards the south during spring. These two tendencies, being equal, would eventually balance one another. The total result, then, must be to diminish the effect of the equatorial protuberance, and therefore to increase the time required for a complete secondary rotation or precession of the equinoxes. Whether the northern preponderance has any effects in determining the axis of the second rotation I am not prepared to say; but it seems to me probable that it has such an influence, and that variations in the direction of the axis may have taken place in past periods of the world's history, as Major-General Drayson suggests, caused by the great upheavals and submergences of land which geology records. The working-out of the problem requires the use of the highest branches of mathematics, with which I am not familiar; but it has been referred to a distinguished mathematician in England. Meanwhile, the facts of the second rotation of the earth on the axis and in the period discovered by Major-General Drayson, with all the remarkable results of the discovery, remain uncontroverted. Quite recently these facts have been verified and established by Admiral De Horsey in a totally independent and original process of investigation and calculation.