258 



NATURE 



[May 25, 1916 



tended ; but the author's colleagues can at least 

 bear witness to the fact that the wonders are 

 described correctly, without exaggeration and 

 without any undue appeal "to the gallery." Dr. 

 Martin has probably been wise to assume that his 

 readers are familiar with chemical formulae, or 

 that, even if they are not, they will still like to 

 see these mystic symbols occupying a place in the 

 text, as evidenfce that the book is a real contribu- 

 tion to chemistry, and not merely a misleading, if 

 popular, exposition. The subjects dealt with 

 include nitrates, explosives, petroleum, coal-tar, 

 alcohol, sugar, and salt, whilst on the more theo- 

 retical side are chapters on radium, on modern 

 alchemy, and on the "mystery of the periodic 

 law." Only in the case of these last-mentioned 

 chapters does any doubt arise as to the ability 

 of the general reader to appreciate the author's 

 exposition ; but that is a question that may soon 

 be solved when the book has circulated as widely 

 as its merits demand. Here and there the burning 

 questions of the day are touched upon — the under- 

 payment of chemical workers generally, and es- 

 pecially of those who are willing to undertake the 

 burden of original research ; the discouragement 

 of research by the undue prolongation of exam- 

 ination tests at the universities ; the loss of the 

 coal-tar industries ; and the risk that freedom of 

 thought may be hampered by the creation of "im- 

 mensely rich and immensely powerful international 

 scientific societies." These questions, discussed 

 in a popular book on the wonders of modern 

 chemistry, may perhaps drive home a lesson which 

 has not yet been fully learned by a public un- 

 versed in the literature of presidential addresses 

 to technical and scientific societies. The book 

 contains thirty-six excellent plates and twenty-nine 

 drawings in the text. T. M. L. 



WIRELESS TRANSMISSION OF PHOTO- 

 GRAPHS. 



Wireless Transmission of Photographs. By 

 M. J. Martin. Pp. xi-t- 117. (London : Wireless 

 Press, Ltd., 1916.) Price 25. 6d. net. 

 'T'HE problem of transmitting pictures by wire- 

 -*- less is not one of actual performance, but 

 of speed of transmission. It is obvious that a 

 "process" picture, one inch square, consisting of 

 some 2000 dots of, say, six different sizes, could 

 be transmitted and set up as " letterpress " in the 

 time it takes to transmit and set up half a column 

 of Nature. The task which Mr. Martin faces is, 

 therefore, the task of bringing the speed of trans- 

 mission within commercially manageable limits. 

 He does this by means of an apparatus which 

 transmits more than 5000 dots a minute. 



This transmission is effected by current impulses 

 produced by the contact of a metal point travelling 

 over a metal positive of the picture, consisting of 

 bichromated gelatine on tin- or lead-foil. Wherever 

 the stylus touches the foil it produces a current 

 impulse in the transmitting antenna. At the re- 

 ceiving station these impulses are photographically 

 recorded on a revolving drum synchronised with 



NO. 2430, VOL. 97] 



the drum on which the transmitted metal picture 

 is fixed. The size adopted is 5 by 7 inches, and 

 the time required for transmission is said to be 

 twenty-five minutes. This is short enough for 

 practical purposes, but very considerable skill is 

 required to prepare the metal prints, and the 

 whole " telephograph " consists of an array of 

 different apparatus, each requiring very careful 

 adjustment. The author acknowledges, indeed, 

 that the process is still in the purely experimental 

 stage. 



The book is useful as giving a general survey 

 of the present state of the problem and some 

 guide towards future experimentation. It should 

 be remarked, incidentally, that the sensitiveness of 

 the Einthoven galvanometer is greatly under- 

 stated, io~^ ampere being quite a strong current 

 for the larger quartz-fibre instruments. Selenium 

 and the preparation of the metal prints are dealt 

 with in separate appendices. The only method of 

 preparing Se cells described is Bell and Tainter's 

 method with brass electrodes, which, of course, 

 are quite unsuitable, and are never used nowa- 

 days. The definition of sensitiveness as the ratio 

 between resistance in the dark and resistance 

 "when illuminated " is too vague to be useful, and 

 should be replaced by some less ambiguous state- 

 ment. 



The electrolytic receiver described on p. 54 as 

 "the most practical and simple of all photo-tele- 

 graphic systems " is remarkably ingenious, though 

 its simplicity is not very obvious. Like the rest of 

 the book, it gives an impression of the great 

 difficulties encountered and the amount of in- 

 genuity already expended on them. 



E. E. F. 



ELECTRICAL ENGINEERING MANUALS. 

 (i) Examples in Magnetism. Second edition. 

 Pp. 90. Price 1. 10 dollars. 



(2) Examples in Alternating Currents. Vol. I. 

 Second edition, with additions. Pp. 223. 

 Price 2.40 dollars. 



(3) H^ow to Make Low-pressure Transformers. 

 Second edition, with additions. Pp. 17. Price 

 40 cents. All by Prof. F. E. Austin. (Han- 

 over, N.H. : Published by the author, 1915" 

 1916.) 



(i) /~^UR opinion of this book is distinctly un- 

 ^^ favourable. The substance is poor in 

 quality, and its quantity is much less than many 

 better books at half the price. In his very first 

 numerical examples the author shows that he has 

 no sound grasp of the real use of numbers in 

 connection with measurements ; and he further 

 displays his deficiency by stating that " i foot- 

 pound exerts a force (our italics) of 13,549,2 13'44 

 ergs," in spite of the satisfactory definition of 

 " force " appearing on the next page. Although 

 he starts with four-figure data (30*48 cm. = i ft., 

 453'6 grams = I lb., ^ = 980 cm. per second per 

 second), he has worked this out to no fewer than 

 ten significant figures ! Such a procedure is 

 unpardonable in one who proposes to "give 



