Art. XVII.—The Comparative Atmospheric Pressure of New Zealand and Great Britain (considered in reference to Dr. Newman's theory of Physical Deterioration).*
[Read before the Wellington Philosophical Society, 26th November, 1876.]
1. In a paper entitled “Speculations on the Physiological Changes which obtain in the English Race when transplanted to New Zealand,” read before this Society on the 30th September last, the author, Dr. Newman, in a very ingenious argument, endeavored to show that in consequence of certain deficiences in the soil and climate of New Zealand, the English race may be expected to deteriorate, both physically and mentally, in future generations. Thus, if Dr. Newman's theory be correct, children born in New Zealand of parents who have migrated hither from Great Britain should be inferior both physically and mentally—taken on an average—to their progenitors, while their descendants in like manner, should deteriorate still further. Dr. Newman goes on to state that indications of this degeneration are even already visible.
2. The alleged deficiencies in the New Zealand soil and climate, to which this supposed deterioration is attributed by Dr. Newman, consist mainly in an insufficient proportion of phosphates as regards the soil and a diminution of atmospheric pressure in respect to the climate. The former of these two points it is not intended to discuss in this paper, the question being one rather for a geological or chemical treatise. Moreover, as Dr. Newman gives us reason to hope that the threatened degeneration from this cause may be averted by so simple and pleasant a prescription as an occasional whitebait dinner or an oyster supper, this aspect of the case may be dismissed.
3. The other hypothetical cause of this hypothetical deterioration must be dealt with more seriously, inasmuch as no course of diet or medical prescriptions would supply greater atmospheric pressure, did any deficiency exist, as it could additional phosphorus, if the soil lacked the needful proportion of that element. It becomes therefore a matter of some moment as affecting the future of this colony, to ascertain whether the atmospheric pressure of New Zealand be really inferior to that of Great Britain as alleged.
[Footnote] * See Newman, Art. V., p. 37.
4. First, let us understand clearly Dr. Newman's arguments on this head. As I understand him, his contention stated in syllogistic form is as follows:—
Major premiss—Children born in countries where the atmospheric pressure is less, have a tendency to be inferior to those born where the atmospheric pressure is greater.
Minor premiss—In New Zealand the atmospheric pressure is less than in Great Britain.
Conclusion.—Ergo, children born in New Zealand should be inferior to those born in England.
5. There is also an implied argument á priori, that inasmuch as this last condition has been observed to exist in certain cases, and as such an effect would be produced by the cause stated in the major premiss, ergo, such cause exists. This last argument it is unnecessary to notice on the present occasion.
6. The object of this paper is, simply, to disprove the minor premiss of Dr. Newman's implied syllogism, and this I hope to be able to do, by showing on indisputable evidence that so far from the atmospheric pressure in New Zealand being less than that of Great Britain, it is in reality appreciably greater.
7. In support of his theory, Dr. Newman correctly states, on the authority of Captain Maury, Dr. Buys-Ballot, and other undoubted authorities in meteorology, that the mean barometric pressure is generally lower in the Southern Hemisphere than in corresponding latitudes of the Northern Hemisphere. This is a fact well known to meteorologists, and thoroughly recognized. At least, if not a “fact” strictly speaking, at any rate all the trustworthy observations hitherto taken tend to prove this to be the case. Mr. Buchan, the Secretary of the Scottish Meteorological Society, in his very able and valuable treatise on this subject,* a standard work which gives the results of observations at 500 different places, situated in almost every part of the globe. From these observations he has constructed a series of yearly, half-yearly, and monthly isobaric charts. In these charts the marked discrepancy between the barometric conditions of the two hemispheres is shown very clearly. In the Northern Hemisphere the isobars follow a most irregular and eccentric course, whereas in the Southern Hemisphere they flow almost in straight lines. It must be remembered, however, that owing to the greater
[Footnote] * “The Mean Pressure of the Atmosphere over the Globe,” “Transactions of the Royal Society of Edinburgh,” Vol. XXV., p. 575.
area of ocean in the latter hemisphere, not only are there fewer local disturbing causes in the shape of spacious continents and lofty mountains, but also the observatory sites are proportionately fewer. Hence the Southern isobars are in many cases merely arbitrary and approximate lines drawn from one point, at which continuous trustworthy observations have been taken, to another similar point perhaps 5,000 or 10,000 miles away, as from the Cape of Good Hope to New Zealand, the intermediate points being furnished by casual intermittent observations made by passing vessels. It is possible that permanent observations, could they be established in as many situations as in the Northern Hemisphere, might necessitate considerable alterations in the isobars at present accepted. However, taking the existing isobars as a standard, we find that whereas the isobar of 30 inches follows a mean latitude of about 42° in the North Atlantic Ocean, the latitude of the same isobar in the South Pacific is only about 35° Similarly, the isobar of 29° 70 inches is found at a mean latitude of about 60° north, and only 48° south. The very low pressure prevalent in the vicinity of Cape Horn is a meteorological feature well known to navigators.
8. All this of course only goes to prove that the mean pressure is less in the Southern than in the Northern Hemisphere. Such in fact might have the form of Dr. Newman's minor premiss, and so stated undoubtedly it would have been irrefragable, but in that case, as the middle term of the syllogism would have been undistributed (it not being shown that the rule included New Zealand as compared with Great Britain), the argument must have fallen to the ground. The real question is—not whether the pressure in New Zealand be less than in the corresponding northern latitudes, but whether it be less than that of England, from whence, to use Dr. Newman's words, the English race is transplanted.
9. Dr. Hahn, of Vienna, in his Essay on the Climate of New Zealand,* says: “It is a well-known fact that the pressure of air decreases very rapidly towards the Pole in the Southern Hemisphere. We find this confirmed in New Zealand, where the medium pressure of air at the level of the sea, between 37° and 46° S. latitude, decreases from 29.981 inches to 29.804 inches; whereas in the Northern Hemisphere in these latitudes the pressure of air remains between 30.009 and 30.001 inches.”
10. Dr. Hahn is not quite accurate here. Reference to the isobaric chart will show that the isobar of 30 inches, which in the Southern Hemisphere lies entirely between latitude 32° in the South Atlantic Ocean, and 40° in the Indian Ocean, in the Northern Hemisphere varies most remarkably,
[Footnote] * Meterological Report, N.Z., 1873, Hector, p. 77.
descending to latitude 30° in the North Pacific Ocean, rising to 55° in North America, descending again to 40° in the North Atlantic, then rising very gradually to latitude 65° in Asiatic Russia, next descending again suddenly to 30° at the starting point.
11. The point, however, is not material to the present argument, excepting so far as it goes to show the existence of such large barometric curves in the Northern Hemisphere where numerous observations have been taken, so that it would not have been an unreasonable hypothesis to suppose the existence of similar curves, if less extreme in degree, in the Southern Hemisphere, where observations are but few. Thus even had New Zealand been in the same latitude in the south as Great Britain in the north, and granting the diminished pressure of the latter hemisphere, it would not have been at all impossible that this colony nevertheless might have enjoyed an atmospheric pressure as large as that of Great Britain.
12. Fortunately, however, authentic observations made in both countries are accessible, and being made under known conditions and with trustworthy and verified instruments are readily intercomparable. Those taken in New Zealand under the auspices of the Meteorological Department, (superintended by Dr. Hector,) comprise the barometric records of fourteen stations, distributed with tolerable evenness over the entire length and breadth of these islands, from Mongonui in the north (latitude 35° 1′) to Southland (latitude 46° 17′), and from Napier in the east (longitude 176° 55′) to Hokitika in the west (longitude 170° 59′), and extending over an average period of about ten years.
13. In order to constitute a fair comparison between the two countries, I have selected the same number of stations (fourteen) in England, Scotland, and Ireland, so distributed as to embrace all parts of the kingdom. Thus in England I have taken Greenwich (London) Liverpool, York, Durham, Clifton, Worthing (Sussex), Stonyhurst (Lancashire), and Helston (Cornwall), at all of which places observations have been made and recorded by the Meteorological Society of England, from whose published returns I have compiled the averages shortly to be quoted. In Scotland I have taken Glasgow, Elgin, and Culloden, where observations are taken similarly for the Scottish Meteorological Society, and published in the journals of that body. The stations in Ireland are Dublin (observations made by Captain Wilkinson, R.E., at the Ordnance Survey Office), Belfast (observations taken at Queen's College), and Armagh (observations by Dr. T. R. Robinson at the Observatory). All these observations are, like those in New Zealand, for a period of about ten years, and in both cases are reduced uniformly to a temperature of 32° Fah. at sea level. The results thereof are entirely comparable.
14. They are as follows:—
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|Great Britain.||New Zealand.|
Difference in favour of New Zealand, 0.07.
15. Hence it is plain that the mean atmospheric pressure of New Zealand, instead of being lower than that of Great Britain, is £07 inch higher, and so disappears the clever but illusive theory built upon the contrary assumption. In comparing the foregoing tables, it is curious to note that the barometric means at the respective English and New Zealand stations of lowest latitude are precisely identical, but the mean, although the highest in great Britain, is not so in New Zealand. The means of the three Scotch observatories, en revanche, are considerably lower than that of Southland, which is the minimum New Zealand mean. It is also noticeable that whereas the lowest latitude of any English observatory is 50° 7′ viz., Helston, in Cornwall, the highest latitude of any New Zealand observatory—that of Southland, for twelve years under my personal charge, and, I believe the most southern in the world—is only 46° 17′. Thus, the most polar New Zealand observatory is 3° 59′ nearer the Equator than the nearest English one, while the nearest New Zealand observatory is no less than 15° closer.
16. Dr. Newman's major premiss I do not intend to discuss in the present paper, although the correctness of his assumption is open to considerable argument. This is the case more especially, inasmuch as it is based to a great extent on another assumption—that pressure increases or diminishes conversely with the degree of atmospheric humidity. A long series of careful hygrometrical observations proves conclusively not only that the two atmospheric conditions are not necessarily correlative, but that often a marked barometric depression is associated with an equally marked atmospheric dryness; at all events, so far from the surface of the earth as
observations can be carried; while a rapid barometric rise, and an influx of moist air also, are frequently coincident. The misapprehension obviously arose from the general acceptance of the theory that the lower pressure of the Southern Hemisphere, as compared with the Northern, is due to the larger relative area of ocean in the former, But that the presence of aqueous vapour is not the only, or even the chief source of deficient pressure, can be proved beyond dispute. Comparison of barometric readings after the subtraction of the vapour tension will show this plainly. A very cogent illustration, however, is afforded by the tables already quoted, which show the pressure to be 29.932 at Hokitika, and only 29.871 at Christchurch, or £061 in favor of the West Coast, notwithstanding that the latter has a mean humidity of £86, as compared with £77 at Christchurch, which, moreover, is to leeward of Hokitika as regards the prevailing wind. Hence the atmospheric pressure seems actually to diminish instead of increasing as the air loses its moisture. The truth appears to be that the atmosphere is subject to disturbances more or less analogous to those of the ocean—waves, currents, eddies, and even tides, produced by causes and governed by laws as yet only imperfectly understood, but wholly irrespective of excess or deficiency of aqueous vapour, whose presence or absence probably is oftener the effect than the cause.
17. There are many other climatological characteristics of New Zealand related directly or indirectly to the subject of Dr. Newman's able essay, and I purpose treating of them on a future occasion. In the present paper I have simply endeavoured to prove—and I trust I have succeeded in the attempt—that whether Dr. Newman's speculations as to the probable degeneration of the English race in New Zealand be well founded or not—for the sake of our adopted country we must hope the latter—at any rate deficient atmospheric pressure does not enter as a factor into the problem.