January 9, 1896] 



NATURE 



221 



of its temperature, is determined by one factor only— the amount 

 of sun-heat it receives. 



How very erroneous is this assumption, may be shown by the 

 contrasted climates of places on the east and west sides of the 

 Atlantic, due to the influence of both ocean-currents and pre- 

 valent winds ; but even more strikingly by a comparison (which 

 I made in my "Tropical Nature") between certain tropical and 

 temperate climates. In Java, about 8° south of the equator, the 

 altitude of the noonday sun in June is about $8^°, while at 

 London during the same month it is 62°, the length of the day 

 at the same time being 5^ hours greater with us. The sun-heat 

 received in London must therefore be considerably greater than 

 that received in Java, and, according to the rule that the aw^««/ 

 of sun-heat determines temperature, London should then have 

 the warmest climate. The fact, however, is that our mean 

 temperature in June is more than 20° lower than that of Java 

 and our mean highest temperature about 18° lower, a result due, 

 as I have shown, to a variety of causes, of which the temperature 

 of the atmosphere in all surrounding aieas, the actfon of aqueous 

 vapour in reducing the loss by radiation, and the accumulation 

 of heat in the soil, are probably the most important. These 

 facts prove, I think, that the amount of heat received by the 

 whole hemisphere, through its influence on both oceanic and 

 aerial currents, must be taken account of in estimating tempera- 

 tures under diflferent phases of eccentricity ; and that any 

 determination of the amounts of sun-heat received at particular 

 latitudes, considered by themselves, are necessarily misleading 

 and must usually indicate a difference of climate far below the 

 truth. 



But there is another consideration of even more importance 

 which entirely invalidates the arguments of those who, like Mr. 

 Culverwell and Prof. Darwin, treat the problem as one to be 

 determined by a simple mathematical calculation of amounts of 

 sun-heat received on the same area at difi'erent times. This is, 

 the remarkable difference in the behaviour of air and liquid 

 water on the one hand and snow and ice on the other, as regards 

 climate ; the former from their great mobility tending to the 

 diflfusion of heat, the latter by its comparative immobility to the 

 accumulation and perpetuation of cold. Without this power of 

 accumulation perpetual snow on tropical and temperate 

 mountains, and glaciers in hot sub-alpine valleys and at only 705 

 feet above the sea-level in latitude 43" 35' south in New Zealand, 

 would be impossible. In either of these cases, if an elevation of 

 about a thousand feet should double the area of the snow fields, 

 which might easily be the case, the outflowing glaciers would be 

 greatly increased in magnitude and might either descend to much 

 lower levels or spread out over large areas of the lowlands — and 

 all this without any change whatever in the total amount of 

 sun-heat received by the countries in which they occur. ^ 



For some years past there has been a persistent attack by 

 astronomers and physicists on the explanation of the glacial 

 epoch put forth by Croll and adopted with some modifications by 

 many students of glacial phenomena. But as these writers have 

 ill treated the problem as a question of the direct effect of the 

 uinount of sun-heat received at different epochs in corresponding 

 latitudes, completely ignoring the great distributing and accumu- 

 lating agencies which are always and everywhere in action, their 

 theoretical conclusions appear to us to be entirely beside the 

 (juestion. We have to deal with a highly complicated problem 

 ill physical meteorology, which cannot be solved by an appeal to 

 ihe well-known facts of the amounts of sun-heat received, any 

 more than can the June climates of London and Batavia or the 

 ;^oneral climates of Ireland and Manitoba or Terra-del-Fuego(in 

 ibout the same latitude) be explamed from similar data. The 

 great merit of Croll was, that he fully realised the complexity of 

 the problem ; that he took account of the various relations and 

 reactions of the oceanic and aerial currents, and the physical 

 characteristics of air and water, snow and ice ; and that he 

 -howed how these causes reacted on each other so that the winds 

 and ocean currents of one hemisphere might have an influence 

 I m the accumulation of snow and ice in the other. Whatever 

 errors he may have made in matters of detail, his method was 

 ■ndoubtedly a sound one, and it is because so many recent 

 \\ Titers on the subject have wholly ignored his method without 

 ven attempting to prove that it is erroneous, that their views 

 cppear to us to lie both retrograde and scientifically unsound. 

 Alfred R. Wallace. 



1 This remarkable property and its effects are explained in some detail in 

 my "Island Life," p. 131 (second edition), under the heading " Properties 

 of Air and Water, Snow and Ice, in Relation to Climate," and in the four 

 following sections. 



NO. 1367, VOL. 53] 



The Dying out of Naturalists. 

 The dying out of the distinguished school of "naturalists"" 

 which this country once produced, and which culminated irk 

 Darwin, is a fact which scarcely admits of dispute. I am in- 

 formed on good authority that it has not escaped the notice of 

 the French scientific world. 



I drew attention to it in the address which I delivered to the- 

 new Botanical Section of the British Association at Ipswich. I 

 rather described the phenomenon than attempted to explain its 

 causes. But what I said has brought me many interestmg com- 

 munications. It has been suggested to me that as far as botany 

 is concerned, I have much myself to be responsible for. It may 

 be so. But this I may say, that in entering the laboratory I did. 

 so with the natural history spirit. I only looked at interesting 

 things with a closer vision. So, if I may go to the other end of 

 the scale, did Darwin when he made use of all the newer ap- 

 pliances of biological research in his later work. 



Nothing, it seems to me, is more difficult than to trace to their 

 right causes the springs of human endeavour. Its results are 

 familiar to us, because we live amongst them. We are so prone 

 to assume "motives" off-hand for any human action that we 

 see about us, that nothing seems easier than to explain any ne^ 

 departure that comes in our way. But the process is almost 

 certainly superficial, and the real causes of asocial change which 

 breaks upon us suddenly have in all probability been of slow 

 growth, and do not at the moment either reveal themselves or 

 readily lend themselves to analysis. 



A friend, a well-known naturalist, gives me his explanation. 

 I suppress his name, as I have not his permission to quote it ;, 

 but I think what he says is worth printing, as affording ground? 

 for reflection. Whether the cause he assigns is or is not well 

 founded, I confess I do not know. 



But generalising from experience I can say this : all dis- 

 tinguished naturalists whom I have known have gone ahead ia 

 defiance of any and every obstacle. Looking back upon their 

 lives, it was as if fate had conditioned them. It was once said 

 to me that if one ever came across a possible artist of merit, the 

 right thing to do would be to offer him every discouragement. 

 If he had real genius he would transcend his ordeals ; it he had- 

 not, the world would not be appreciably the poorer if he was- 

 quenched. 



But I must discriminate. English naturalists of the generation 

 which is now passing away have belonged to two groups. Some 

 have been born to wealth, some to poverty. Class prejudice 

 was against the one ; means of livelihood against the other_ 

 The richer disciples of our art seem now to have gone irre- 

 trievably, and to have no successors. The poorer have changed 

 their tone ; they tend to treat science as a career like the Civil. 

 Service. They approach those who have any hand in the matter 

 in an extremely business-like spirit. I do not blame them. But 

 this is not the initier of the scientific hero. Nor in their memory 

 shall we assemble to found a national memorial or raise a statue. 

 What is the force that now-a-days quenches the old enthusiasm?' 

 My correspondent says that it is the schools, and here is his 

 story. I believe that, at any rate, what he says is the outcome 

 of sincere conviction, or I would not publish it. 



" I am pleased to see your remarks upon the dying out of the 

 study of systematic botany, and I see in other papers, too, atten- 

 tion called to this and the diminution of field naturalists. One 

 starts one's natural history usually on these lines when a boy — 

 or, rather, used to— but I noticed things had altered much when 

 I visited my old school last winter. In my day we had lots of 

 naturalist boys ; we knew all the localities for insects, plants, 

 shells, &c. Now hardly any one knows anything of the country 

 beyond the playing fields. The 'skipper field,' famous for 

 skipper butterflies ; the heath, with its localities for all kinds of 

 insects and plants, are absolutely unknown. The great object 

 of education appears to be to have every boy competing for 

 something absolutely useless to him in later life. They were 

 practising cricket or other games, or cramming for exams, al 

 the while. This remarkable system begins, the masters of this 

 and other schools told me, at about eight years old. There is 

 no time to learn to think or observe. The boys must beat some 

 other school in tennis or football, or must beat some one else in 

 the history of the Punic Wars. Science was taught, but much 

 in the same way. They were neither taught, nor did they get a 

 chance of teaching themselves, any natural history. What the 

 result of this will be it is difficult to foresee, but it certainly 

 accounts a good deal for the diminution in systematists and field- 

 naturalists." W. T. Thiselton-Dyer. 

 Royal Gardens, Kew, December 27, 1895. 



