32 



NATURE 



\_Nov. II, 1880 



only by divesting the mind of all metaphysical vagaries, 

 and approaching the discussion in a spirit of strict loyalty 

 to the established principles of evolution. The universe 

 is not "a mental phenomenon," as Schopenhauer would 

 call it, nor is speech the deliberate product of conscious 

 will. It is an organism which, hke all other organisms, 

 had its origin in a germ, and its slow growth and silent 

 development in suitable surroundings, independently of 

 all conscious action. Yet in dealing with a subject of this 

 sort one still feels how much easier it is to refute error 

 than to establish truth. "Uiinain tain facile vera invenire 

 possim quam falsa conviiicere" A. H. Keane 



OUR BOOK' SHELF 



Easy Lessons in Science. Edited by Prof. F. W. Barrett. 

 I. Easy Lessons in Heat. By C. A. Martineau. II. Easy 

 Lessons in Light. By Mrs. W. Awdry. (London : 

 Macmillan and Co., 1S80.) 



These excellent little lesson books deserve a wide circu- 

 lation. Well and clearly written, they are at the same 

 time strictly of the " scientific " rather than of the so- 

 called "popular" style of exposition; there being none 

 of the objectionable sensational element with which 

 certain French works in light science have too greatly 

 familiarised us. The cuts with which the volumes 

 before us are illustrated are numerous, appropriate, and 

 many of them original. In each case the reader is in- 

 structed in the simple apparatus needed to repeat the 

 experiments described ; so that a teacher who desires to 

 give to young pupils a few elementary lessons in the 

 sciences of heat and light will find here the very text- 

 books most suited to his requirements. Miss C. A. 

 Martineau's " Lessons in Heat " follows the usual order 

 of text-books in that science. The first lesson deals with 

 expansions, the second with notions of temperature, the 

 third tells "how heat spreads," and so forth, and in the 

 concluding chapters some of the fundamental facts of the 

 relation between heat and mechanical work are made 

 known. One experiment which we do not remember 

 meeting with before in the shape in which it is given 

 deserves to be cited. It is a variation on Davy's old 

 experiment with flame and gauze. " Put a bit of camphor 

 on the wire gauze, and hold a light under it. The vapour 

 of the camphor passes freely through the gauze, catches 

 fire, and burns with a blue flame till the whole of the 

 camphor has been turned into vapour and burned. But 

 the flame does not pass through the gauze to set fire to 

 the solid camphor." 



Mrs. Awdry's "Lessons on Light" are no less felicitous 

 in their treatment of the subject. The usual popular text- 

 book on Optics abounds in descriptions of different optical 

 instruments, telescopes, microscopes, kaleidoscopes, and 

 the like, without much trouble being expended upon first 

 principles. But in these lessons first principles claim 

 the prominent place : the first point explained is the law 

 of inverse squares, and the second the geometrical laws of 

 refraction and reflection — and the explanations are ad- 

 mirably yet quite simply done. A most interesting feature 

 is that the latter half of these easy lessons is devoted to 

 physical optics. Cine chapter on the wave-theory, and 

 two entitled " Measurings" prepare the way for a capital 

 lesson on Diffraction. A lesson on the Spectrum and 

 one on the Rainbow close the series. 



We do not say that there is no room for criticism in 

 judging these little volumes. A professed teacher of 

 Natural Philosoph)- might grumble at the omission of 

 certain things that claim prominence in all the older text- 

 books and in many of the syllabuses of contemporary 

 examinations. Yet we would challenge such critics to 

 produce a more useful, or suggestive, or accurate set of 



lessons, or one more entirely free from the two besetting 

 faults of sensational popularisation and educational cram. 

 It is to be hoped that Prof. Barrett will continue his 

 labours in adding to the series he has so ably edited. 



Outline of a Course of Natural Philosophy, with Speci- 

 men Examination Papers. By Gerald MoUoy, D.D. 

 (London: Simpkin, Marshall, and Co., 18S0.) 



This work of 114 pages contains a syllabus-outline of 

 the course of lectures in Natural Philosophy by Dr. 

 MoUoy, at the Catholic University of Ireland, and is 

 reprinted chiefly to meet the wants of teachers in inter- 

 mediate schools. To the syllabus, which is remarkably 

 full and complete, is appended an extensive series of 

 examination papers on all branches of physics except 

 light, electricity, and magnetism, which are promised to 

 follow. These questions, though chiefly elementary, have 

 been carefully prepared, and are a valuable part of the 

 work. In an appendix Dr. Molloy reprints a paper 

 giving an account of his particular form of bichromate 

 battery, which appears to be peculiarly suited to the needs 

 of schools and colleges, where a powerful battery of 

 convenient form is required to be in readiness for occa- 

 sional use. 



LETTERS TO THE EDLTOR 



[The Editor does not hold himself responsible for opinions expressed 

 by his correspondtnts. A'eithcr can he undertake to return, or 

 to correspond with the writers of, rejected manuscripts. No 

 notice is taken of anonymous communications.'] 



[ The Editor zirgently requests correspondents to keep their letters as 

 short as possible. The pressure on his space is so great that it 

 ts impossible otherwise to ensure the appearance even op com- 

 mtinieations containing interesting and novel facts.] 



Sir Wy villa Thomson and Natural Selection 



I AM sorry to find that Sir Wyville Thomson does not under- 

 stand the principle of natural selection, as explained by Mr. 

 Wallace and myself. If he had done so, he could not have 

 \\ritten the following sentence in tlie Introduction to the Voyage 

 of the Challenger: — "The character of the abyssal fauna refuses 

 to give the least support to the theory which refers the evolution 

 of species to extreme variation guided only by natural selection." 

 This is a standard of criticism not uncommonly reached by theo- 

 logians and metaphysicians, when they ^vrite on scientific subjects, 

 but is something new as coming from a naturalist. Prof. Huxley 

 demurs to it in the last number of Nature ; but he does not 

 touch on the expression of extreme variation, nor on that of 

 evolution being guided only by natural selection. Can Sir 

 Wyville Thomson name any one who has said that the evolution 

 of species depend, only on natural selection? As far as concerns 

 myself, I believe that no onehasbrought forward so many observa- 

 tions on the effects of the use and disuse of parts, as I have done 

 in my " Variation of Animals and Plants under Domestication " ; 

 and these observations were made for this special object. I 

 have likewise there adduced a considerable body of facts, showing 

 the direct action of external conditions on organisms ; though no 

 doubt since my books were published much has been ;learnt on 

 this head. If Sir Wyville Thomson were to visit the yard of a 

 breeder, and saw all his cattle or sheep almost absolutely true, 

 that is, closely similar, he would exclaim : "Sir, I see here no 

 extreme variation ; nor can I find any support to the belief that 

 you have followed the principle of selection in the breeding of 

 your animals." From what I formerly saw of breeders, I have 

 no doubt that the man thus rebuked would have smiled and said 

 not a word. If he had afterwards told the story to other 

 breeders, I greatly fear that they would have used emphatic but 

 irreverent language about naturalists. Charles Darwin 



Down, Beckenham, Kent, November 5 



