270 



NATURE 



[December 291, 1910 



is the duty of philosophers to go on trying to make 

 them, with which, no doubt, both pragmatists and 

 absolutists would agree. Indeed, " in spite of every- 

 thing, this is presumably the real standpoint of all of 

 us." 



Lessons on Elementary Hygiene and Sanitation, with 

 Special Reference to the Tropics. By VV. T. Prout. 

 Second edition, 1909. Pp. xx+159. (London: J. 

 and A. Churchill, 1908.) Price 2s. 6d. net. 



We are not surprised that this little book has passed 

 into a second edition. The plan of it is well conceived 

 and the matter excellently written. It tells in the 

 simplest language, with many appropriate compari- 

 sons which drive home the meaning, the structure of 

 the body and its functions, how health may be safe- 

 guarded, and how disease is propagated. Disease 

 germs, their mode of spread and entrance into the 

 body, are explained, and the salient points with re- 

 gard to the principal infective diseases are adequately 

 considered. Being avowedly written for residents in 

 the tropics, and in particular for those in Freetown, 

 West Africa, diseases like malaria, cholera, plague, 

 sleeping sickness, leprosy, &c., receive considerable 

 attention, but otherwise the details given are equally 

 applicable to the hygiene of any district. 



Chapters on water supply and its purification, the 

 dwelling and sewage removal, respiration and ven- 

 tilation, diet and clothing are included, and render 

 the book a complete popular exposition of the prin- 

 ciples of hvgiene. It is also well and sufficiently 

 illustrated. ' R. T! H. 



Aeroplane Patents. By Robt. M. Neilson. Pp. x + 

 91. (London : Constable and Co., Ltd., 1910.) 

 Price 4s. 6d. net. 



This is a useful book, which may be recommended to 

 all who are interested in the subject of aeronautics. 

 It begins with thirteen pages of sound advice to in- 

 ventors, and continues vi^ith a list and description of 

 the various patents relating to heavier-than-air flying 

 machines. The list does not profess to be complete 

 or exhaustive, but it contains all the important patents 

 and most of the minor ones are mentioned. The de- 

 scriptions given are sufficient to explain the objects 

 and claims made in each case. 



The period covered by the list extends from i860 to 

 1910, and perhaps the most interesting matter which 

 it brings to our notice is the enormous increase in 

 the number of patents relating to aeronautics taken 

 out since 1907. From i860 to 1906 the average 

 number of patents was about six per year. In 1906 

 the number was 29 ; in 1907, 42; in 1908, 115; in 

 1909, 759; and in 1910 (for eight months), 412. 



That but a small percentage of the patents should 

 be of value is only what might be expected, but the 

 total number is evidence of the attention which is 

 being given to the subject. 



Stray Leaves on Travel, Sport, Animals, and Kindred 

 Subjects. By J. C. Walter. Pp. xii + 295. (Lon- 

 don : Kegan Paul, Trench, Triibner and Co., Ltd., 

 1910.) Price 55^. net. 



The ten chapters making up this book are for the 

 most part extracts from the author's diaries written 

 among the scenes described, and papers prepared for 

 meetings of a natural history society. 



The conversational style adopted makes reading 

 easy, and the persevering reader will incidentally accu- 

 mulate much useful information about the countries 

 in which the author has travelled, and become 

 acquainted with the habits of many animals which 

 have aroused the author's interest. Mr. Walter's 

 wanderings have by no means been confined to his 



NO. 2148, VOL. 85] 



own country; we have chapters dealing with his excur- 

 sions in Egypt and Palestine, France, Switzerland, 

 and Italy respectively. On each of his numerou- 

 journeys Mr. Walter was an industrious diarist. 



1200 Mining Examination Questions. Arranged and 

 compiled bv G. L. Kerr. Pp. xxvii+iii. (Lc 

 don : Crosby Lockwood and Son, 1911.) Pri 

 2s. 6d. net. 



These questions have been selected principally from 

 the papers set at the examinafTons held in the different 

 districts of Britain for managers' and under-managers' 

 certificates. The volume also contains copies of venti- 

 lation plans set at these examinations, and suggestions., 

 to candidates who desire to qualify for mine managers* 

 certificates. 



To some of the questions answers have been given, 

 but to the majority of them this has intentionally not 

 been done. The compiler explains that the correct 

 answer for any given question will vary somewhat 

 according to the formula used, and in mining unfor- 

 tunately no uniform set of formulae has yet been • 

 accepted. 



Chez les Francais. Edited by H. Carter. With] 

 Exercises, by C. F. Shearson. Pp. vii+171 + vii. 

 (London : A. and C. Black, 1910.) Price 2s. 



This well-selected collection of passages in French,] 

 from writers of recognised literary merit, dealing with^ 

 France and French customs, should prove useful in : 

 classes where some progress has been made in the 

 study of the language. The book should be particu- 

 larly serviceable in connection with elementary 

 geographical teaching. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opiniom 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected , 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.^ 



A Biological Inquiry into the Nature of Melanism in 



Aiiiphidasis betularia, Linn. 



It is well known to entomologists that dark varieties 

 of several species of moths have recently become increas- 

 ingly common in many localities within the British Isles, 

 and also that the dark forms are appearing in fresh 

 districts. 



It is very desirable and important to know whether th& 

 colour of these dark races of moths is protective or whether 

 it has some other significance. 



Before, however, anj' definite explanation of these 

 phenomena can be attempted, it is necessary to have as 

 complete a knowledge as possible of all the circumstances 

 which are likely to have any influence on the species 

 known to exhibit this melanic change. One significant 

 point in connection with my inquiry concerns the resting 

 habits of the moths which are subject to this melanic 

 variation. For example, it is important to know whether 

 the light-coloured moths (i.e. the peppered form of Ampki- 

 dasis betularia) generally rest during the day on lichen- 

 covered trunks of trees or any other light-coloured object, 

 and also whether the dark insects (as the form 

 Doubledayaria of .4. betularia) select black tree trunks or 

 other dark-coloured objects on which to rest. 



Information of this nature can, however, be obtained 

 only by the cooperation of very many entomologists, for 

 the chance of obtaining sufficient evidence from the 

 observations of one or two persons is very remote. _ I 

 should therefore be extremely grateful if entomologists 

 would assist me in collecting information regarding the 

 resting habits of any of the undermentioned species belong- 

 ing to the Geometrae which may have come under their 

 notice : — ' 



