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THE POPULAR SCIENCE MONTHLY. 



pungent herbs are noxious to them; but 

 nettles are a favorite haunt of certain small 

 land-shells. Spring is the most active sea- 

 son for snails ; they attain their fullest de- 

 velopment toward midsummer ; and as win- 

 ter approaches they penetrate the ground or 

 in warm regions attach themselves to the 

 bark of trees or to stones for a period of 

 hibernation. They close the aperture of the 

 shell with a leathery secretion, sometimes 

 strengthened by more or less limy matter, 

 or, if naked, may surround themselves with 

 it like a cocoon. 



Value of Scientific Amateurs. — Is it not 



true (asked Prof. Arthur Schuster in the Brit- 

 ish Association) that the one distinctive feat- 

 ure which separates England from all other 

 countries in the world is the prominent part 

 played by the scientific amateur, and is it not 

 also true that our modern system of educa- 

 tion tends to destroy the amateur ? By ama- 

 teur I do not necessarily mean a man who 

 has other occupations and only takes up 

 science in his leisure hours, but rather one 

 who has had no academical training, at any 

 rate in that branch of knowledge which he 

 finally selects for study. We may, perhaps, 

 best define an amateur as one who learns his 

 science as he wants it and when he wants it. 

 I should call Faraday an amateur. He would 

 have been impossible in another country ; 

 perhaps he would be impossible in the days 

 of the Science and Art Department. Other 

 names will occur to you, the most typical and 

 eminent being that of Joule. We are in 

 danger of losing one great and necessary fac- 

 tor in the origination of scientific ideas. If 

 I am right, there is a distinct advantage in 

 having one section of scientific men begin- 

 ning their work untrammeled by precon- 

 ceived notions, which a systematic training 

 in science is bound to instill. If school ex- 

 aminations could be more general, if scien- 

 tific theories could only be taught at an age 

 when a man is able to form an independent 

 judgment, there might be some hope of re- 

 taining that originality of ideas which has 

 been a distinctive feature of this country, 

 and enabled our amateurs to hold a promi- 

 nent position in the history of science. At 

 present a knowledge of scientific theories 

 seems to me to kill all knowledge of scientific 

 facts. It is by no means true that a com- 



plete knowledge of everything that has a 

 bearing on a particular subject is always ne- 

 cessary to success in an original investiga- 

 tion. In many cases such knowledge is es- 

 sential, in others it is a hindrance. Different 

 types of men incline to different types of re- 

 search, and it is well to preserve the dual 

 struggle. 



What caused the Ice Age ? — In their pa- 

 per in the British Association on The Cause 

 of the Ice Age, Messrs. P. F. Kendall and J. 

 W. Gray maintain that the Glacial period 

 came on with extreme slowness ; that it was 

 of long duration ; that it passed away very 

 abruptly and very recently, probably about ten 

 thousand years ago ; and that the geological 

 record, though yielding evidence of ancient 

 glaciers, yet was without trace of any previ- 

 ous Glacial period. They criticised the ex- 

 isting theories of the cause of the Ice age, 

 and urged that the ingenious theory of Croll 

 was objectionable upon several grounds. It 

 was linked with a chronology which, even 

 with the reservations made by Sir Robert 

 Ball, was not reconcilable with geological 

 facts. It involved the occurrence of repeat- 

 ed Glacial periods, and accounted neither for 

 the very gradual approach nor the very abrupt 

 departure of the cold. The theory of Mr. 

 Upham, of the United States Geological Sur- 

 vey, that a great series of continental uplifts 

 had raised enormous areas of the Northern 

 Hemisphere above the snow-line, was based 

 on evidence valid in itself, but failed to prove 

 that the uplift was synchronous or coincided 

 with the Glacial period. Further, there was 

 irrefragable evidence that the British Isles 

 stood at almost absolutely the same level as 

 at present. Enormous ice-sheets swathed the 

 whole of the northern and western portions 

 of Britain. An explanation which would not 

 apply to the British Isles might safely be re- 

 jected. The authors, although they formu- 

 late no theory of their own, invite the atten- 

 tion of astronomers to the suggestion that 

 as the sun has undergone a secular cooling 

 such as the president, Sir Archibald Geikie, 

 declared in his address had happened to the 

 earth, the Glacial period was a consequence 

 of this cooling. This would perhaps account 

 for the gradual refrigeration, leaving not the 

 Ice age, but the genial period which sudden- 

 ly supervened, to be accounted for. Varia- 



