Nov. 28, 1878] 



NATURE 



71 



Enough has been said to show the extreme value of the 

 book to the scientific botanist. May its teachings quicken 

 sound study in England. MARCUS M. Hartog 



OUR BOOK SHELF 



Manuel du Voyageur. Par D. Kaltbrunner, Membre de 

 la Societdde Geographic de Geneve. (Zurich, J. Wurster 

 und 0% Editeurs. Paris, C. Rheinwald und C'S 1879.) 

 A GREAT difficulty of writing a treatise for the use of 

 travellers, on "What to Observe," lies in the impossi- 

 bihty of presenting to the imagination an ideal average 

 traveller to address. If the great mass of intending tra- 

 vellers had much the same amount of scientific knowledge 

 and were well grounded in the elements of science gene- 

 rally, a very useful and compact work might, no doubt, 

 be composed. But as a matter of fact such persons are 

 usually very ignorant, or variously ignorant, and a 

 book fitted to instruct the whole of them must omit 

 none of the more elementary considerations, and there- 

 fore would assume the shape of a collection of encyclo- 

 paedic treatises. It is hard to define the level of previous 

 knowledge to which " Kaltbrunner's Manuel du Voyageur " 

 is best adapted. Every reader is sure to think it too 

 diffuse for his own wants in some parts, neither deep nor 

 full enough in a great many, and probably beyond his 

 depth in others ; but take it all in all, it is perhaps better 

 adapted for persons of moderate culture than any similar 

 book that could be named. It is beautifully got up, with 

 abundant illustrations, and to say the least, would be often 

 iiseful for reference and as a reminder. The range of its 

 topics is wide enough to touch the interests of everybody, 

 and it would be a capital present to give to a friend 

 bound for foreign parts. Considerable space is allotted 

 to subjects connected with social life and other anthro- 

 pological questions. 



There seems to be some irony in the fact that when the 

 world is so nearly explored, manuals for the use of tra- 

 vellers should begin to appear. They were greatly 

 needed many years ago, when the Admiralty Manual 

 had the field nearly all to itself, but now that the need 

 is less, these works are at last composed in abimdance. 

 The present one, however, is by no means intended to 

 supply the wants of those travellers only who are explor- 

 ing unknown coimtries, much of it being applicable even 

 to home districts. It is less solid and more compre- 

 hensive than the recent German publication, "Anleitimg, 

 &c.," by Neumayer. 



Pleasant Ways in Science. By R. A. Proctor. (London : 

 Chatto and Windus, 1879.) 



Of this book, which has been sent me for review, I can 

 truly say that it is an excellent specimen of what has been 

 well called (I forget by whom) Paper Science. A very 

 few quotations will amply justify this verdict. 



At pp. 8, 152, I find "heat" several times standing 

 for " temperature." But the author (in these columns, 

 vol. xvi. p. 227) insisted that 



" What mathematicians call the moving force exerted by the 

 earth on the moon is eighty-one times greater than the corre- 

 sponding force exerted by the moon on the earth." 



To put "heat" for "temperature" is after all not 

 very strange for one who puts " moving force " for 

 " accelerating force." 



In the account given of the experiments of Andrews 

 and Tait on ozone, the action of " iodine" is given as 

 that of " mercury " : and the now-received idea of the 

 nature of ozone — though twice mentioned in the paper 

 referred to— is described as a " beautiful " and " in- 

 geniously conceived" hypothesis suggested after the 

 publication of the paper (pp. 351-2). 



The following passage, which refers to friends 'of my 

 own, I quote without comment : — 



" .... no one, I think, would believe so ill of his 

 fellow-men as to suppose for one moment that advan- 

 tage could be taken of the sympathies which have been 

 aroused by the Indian famine, or which may from time 

 to time be excited by the record of great disasters by sea 

 and land, to advocate bottomless schemes tmrely for pur- 

 poses of personal advancement. We must now, perforce., 

 believe that those who advocate the erection of new 

 observatories and laboratories for studying the physics of 

 the sun have the most thorough faith in the scheme which 

 they proffer . ..." (p. 51). 



From p. 194 I gather that I know nothing about the 

 motion of waves, and p. 240 proves me equally ignorant 

 of voltaic electricity. I cannot read any more. 



P. G. T. 



LETTERS TO THE EDITOR 



\^The Editor does not hold himself responsible for opinions expressed 

 by his coirespondents. Neither can he undertake to return, »r 

 to correspond vnth the writers of, rejected manuscripts. No 

 notice is taken of anonymous communications. 



[The Editor urgently requests correspondents to keep their letters as 

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

 is impossible otherwise to ensure the appearance even of com- 

 munications containing interesting and noz'el facts.l 



Receiving Telephones 



I HAVE roughly tried two experiments which seemed likely 

 to supply new forms of receiving telephones, and have had such 

 partial success as seemed satisfactory in preliminary trials. As 

 I have not time to continue the experiments I request the inser- 

 tion of this note in the pages of Nature, in the hope that some 

 one else will follow the matter up. 



In one experiment a spiral wire (I used German silver, but it 

 may be of any material) was wound closely so that the spires 

 were in contact, or nearly so. One end of the spiral was fixed 

 and the other end attached by a thread to the middle of a small 

 parchment drum-head, such as is sold by the toy-makers for 

 thread telephones. A slight tension was put on the thread to 

 draw the spires of wire slightly asunder. The spiral wire was 

 then made part of a circuit, including one or two ceUs of Grove's 

 battery and a line wire going to another room. By this appa- 

 ratus such sounds as the scraping on a file were satisfactorily 

 heard, although the spiral was only one coil of about an inch 

 long. It will be observed that in this arrangement there are no 

 magnets ; the whole effect is produced by the varying induction 

 of the current upon itself. The apparatus could obviously be 

 rendered more efficient by using a longer spiral, or a coil con- 

 sisting of a number of concentric spirals not quite in contact, so 

 as to allow small motions to exist. The induction might be 

 still farther increased by using a spiral of two wires, so that a 

 powerful local current might be kept up in the alternate spires, 

 while the varying line-current is passing through the inter- 

 mediate ones. Another improvement would consist in using 

 iron wire wound in a sufficiently loose coil. The self-magneti- 

 sation of this coil would co-operate with the electric induction to 

 heighten the eflFect. 



In the other arrangement an iron or steel spiral (in my experi- 

 ment it was an ordinary steel spiral spring, of which the spires - 

 lay close) was placed inside a coil of copper wire in circuit with 

 a battery and the line. The spiral, as before, was fixed at one 

 end, and kept slightly stretched by a string connecting its other 

 end to a drum-head. In this arrangement no cmrent passes 

 through the spiral, but it is the core of an electro-magnet, and 

 becomes magnetised in a degree which changes with the altera- 

 tions in the intensity of the line-current. This causes the spires 

 to attract one another with varying intensity, and the tremulous 

 motion so produced is propagated by the string to the parch- 

 ment. By this arrangement singing, whistling, &c., were 

 heard when a Reiss transmitter was used. Probably a soft iron 

 coil would have been better than the steel spring I used, and the 

 apparatus is susceptible of other obvious improvements which 

 would add to its sensitiveness. 



Before concluding permit me to thank Prof. Barrett for 

 allowing me to make the experiments in his laboratory. 



Dublin, November 25 G. JOHNSTONE SxoNKT 



