June 12, 1890] 



NATURE 



147 



claims of education in natural history as a means to 

 individual and mutual happiness are perhaps too well 

 known to need assertion ; at any rate, it is not fashionable 

 to put them forward. 



For schools, one would like in this book a little more 

 of the breath of the open country, such as appears in the 

 few lines descriptive of the Cotteswolds ; but the direct 

 appeal to Nature in chapter ix. is very refreshing and 

 characteristic of the author. Where, indeed, the work 

 has been altered from the first edition of 1863, it is in 

 matters of more recent discovery, its tone being fully 

 preserved. Some little notes have gone, such as that on 

 the difficulties of the Welsh " 11 " on p. 216 of the original 

 (p. 261 of the present edition is more serious) ; but the 

 references to history and familiar authors remain, even to 

 Wilkie Collins, while the introduction of derivations has 

 been considerably and interestingly extended. Quaint 

 effects in such matters cannot always be avoided, as in 

 the following (p. 247), " lUaenus {squint-eye) Davisii {after 

 Mr. Davis)." 



It is difficult in such a book to deal with rival theories ; 

 but the discussion of coral-islands, carried over seven 

 pages, scarcely does justice to Darwin's position, and 

 is certainly not complete — as in accounting for the atoll — 

 in its statement of more recent views. Nor can we con- 

 sider the treatment of the specific gravity of the earth 

 (p. 8) as altogether beyond question, accepting as it does 

 the continuous compressibility of crystalline bodies. 



To come to small matters, the use of " potash " in 

 different senses on pp. 46 and 48 may mislead the tyro ; 

 the spelling " tachylite" is adopted for " tachylyte " ; and 

 " Protospongia fenestella" for "fenestrata" occurs on 

 both p. 238 and p. 239. On p. 329 we have, freshly 

 inserted, the Pterodactyl from Owen's "Palaeontology." 

 This figure, arising from the difficulty of interpreting 

 some of the earlier specimens, still appears in well- 

 regulated text-books, but is sometimes accompanied with 

 warning foot-notes ; here it is aggravated by having its 

 digits numbered, and the existence of a fifth, "answer- 

 ing to the little finger in our own hands," is distinctly 

 stated in the text. But the other woodcuts are numerous 

 and effective ; and we have a few bold drawings of natural 

 features as they actually appear, which always appeal 

 strongly to the untrained observer. It is too much to ask 

 for full-page sketches of our British scenery ; but we look 

 back in this matter somewhat regretfully on that earlier 

 work of Jukes, the " Popular Physical Geology," illus- 

 trated by Du Noyer, and published with undoubted spirit 

 by Reeve and Co. in 1853. G. C. 



OUR BOOK SHELF. 



Magnetism and Electricity, By W. Jerome Harrison, 

 F.G.S., and Charles A. White. (London: Blackie 

 and Son, 1890.) 



We note one or two features in this work which make it 

 worthy of commendation ; for example, the authors have 

 avoided speaking of magnetic or electric fluids, and have 

 endeavoured to bring out the fact that these forces are 

 but " states or affections of matter," and their endeavour 

 is much to be praised. It is also good to see an intro- 

 ductory chapter on " Matter and Force," and a special 

 chapter on " Potential," about which elementary students, 

 as a rule, know very little. Most of the diagrams, how- 



NO. 1076, VOL. 42] 



ever, are of the stock kind, and with the exception of the 

 above points the book possesses nothing to distinguish it 

 from many other elementary manuals dealing with the 

 same subject 



Science applied to Work. By John A. Bower. (London : 



Cassell and Co., 1890.) 

 There is much that is praiseworthy in this little work; it is 

 an easy introduction to mechanics, and free from all mathe- 

 matical formula;, is written in very clear language, and 

 deals entirely with the mechanics of every-day life. The 

 book has been designed especially for the artisan section 

 of the National Home Reading Union, and will doubtless 

 be a means of eradicating the rule-of-thumb work which 

 is still characteristic of a large proportion of the artisan 

 community. Many hints are given for making simple ap- 

 paratus to demonstrate the principles laid down, the ap- 

 pHcations of these principles are well pointed out, and the 

 work altogether meets the requirements of the class for 

 whom it is intended. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed 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. ] 



Testing for Colour Blindness. 

 Dr. Oliver Lodge asks (May 29, p. loo) why those in- 

 terested in testing for colour-vision do not employ Lord Ray- 

 leigh's arrangement, in which yellow is matched by certain 

 proportions of red and green. 



This suggests to me a difficulty I have felt for many years. I 

 am partially colour-blind, and have the usual difficulty in seeing 

 whether a fuchsia or a Pyrus faponica is in flower or not. I 

 have noticed that many persons speak of flowers such as Lychnis 

 fios-Jovis, or Epilobium angustifolium, &c., as being red. I 

 should unhesitatingly class them among blue or purple flowers. 

 Tliey give me no suggestion of red, but I observe that when thev 

 are coloured in botanical works, such as Sowerby's " Botany," 

 «&c., they are painted of a decidedly reddish colour, and not as 

 they appear in Nature. I used to attribute this to carelessness, 

 but it is now evident to me that two colours which when placed 

 side by side appear identical to normal vision do not appear at 

 all identical to the colour-blind. Doubtless pigments could be 

 found which would produce similar impressions on both orders 

 of vision, but this is only a matter of chance. An investigation 

 on these lines might give useful information. 



On the question of flag signals, I would observe that though 

 I can make nothing out of the ordinary dull greens, reds, and 

 browns, and am ready to believe anything that is told me about 

 them, my impressionsof scarlet and orange are intensely distinct 

 and vivid. Scarlet (and especially orange scarlet) is the most 

 vivid and beautiful colour which I know, and utterly unlike any 

 other (it turns to nearly black in very faint twilight). I could 

 recognize a flag of scarlet or orange under any possible circum- 

 stances and at almost any distance. If danger flags had this 

 colour they would perfectly suit the colour-blind, and could 

 never be mistaken for green. 



On the subject of night signals I cannot make a useful sug- 

 gestion. Green lights are very distinct, but they appear to me 

 as a poor blue with very little power in them. Red lights are 

 distinct enough compared side by side with ordinary yellow 

 ones, but seen alone under unfavourable circumstances there is 

 nothing to catch the eye or the imagination, and they might 

 easily be mistaken for yellow or ordinary lights. 



London, June 9. Latimer Clark. 



Coral Reefs — Snail Burrows. 

 In regard to Dr. von Lendenfeld's letter (May 29, p. 100) it 

 may suffice for me to say that I had not seen his reviews of 

 Darwin's "Coral Reefs" in the periodicals which he names (for I 

 find it impossible to keep level with the advancing flood of 

 scientific literature), and that if his reply "considerably modifies 



