500 



NATURE 



[January 7, 19 15 



a survey is obvious not only to the man of science, 

 but to the technical leather trades chemist who 

 is always seeking some new tanning material in 

 view of the probable early exhaustion of some of 

 the materials now in common use. A chapter on 

 the physiological rdle played by the tannins in the 

 plant concludes the botanical part of the book, 

 and gives a very interesting account of the work 

 done on this difficult subject. 



The researches of Emii Fischer and his pupils 

 on the chemistry of the tannins have robbed the 

 earlier work on the subject of much of its interest, 

 and the author might have gone further in cutting 

 down his account of this older work, which will 

 only rarely bear criticism and is scarcely ever 

 suggestive of further work. This applies even to 

 the formula which the author himself suggested 

 for gallotannic acid, 



C6H2(OH3).C(OH).O.CO.C6H(OH)3, 

 a constitution which is merely the tautomeric form 

 of that suggested by Bottinger for oakwood 

 tannic acid, 



C6H2(OH)3.CO.C6H(OH)3.COOH. 

 This fact is not alluded to by Dr. Dekker, or 

 by other authors who have discussed Dekker's 

 formula. 



An excellent bibliography of tannin literature, 

 comprising all books published since 1571, and 

 all papers since 1754, forms one of the most valu- 

 able features of the book. All who intend work- 

 ing on the chemistry or chemical technology of 

 tannins will find here a valuable guide to original 

 work on the subject. Dr. Dekker also gives 

 accounts of no fewer than eighty-six methods of 

 tannin analysis. This part of his book is of 

 great interest to leather trades chemists. The 

 same cannot be said of the chapter on practical 

 tanning, which would have been better omitted. 



Dr. Dekker's book can be thoroughly recom- 

 mended to all botanists, chemists, or technologists 

 who are specially interested in vegetable tannins, 

 as it is certainly the best and most complete 

 account existing of our knowledge of these bodies. 



E. S. 



WIRELESS TELEGRAPHY. 



(i) Text-book on Wireless Telegraphy. By Prof. 

 R. Stanley. Pp. xi + 344. (London : Longmans, 

 Green and Co., 1914.) Price 75. 6d. net. 



(2) Wireless Telegraphy : a Handbook on the 

 Fundamental Principles and Modern Practice of 

 Radio-telegraphy. By A. B. Rolfe-Martin. Pp. 

 vi + 256. (London: A, and C. Black, 1914.) 

 Price 55. net. 



THE literature of wireless telegraphy has 

 already become very extensive although the 

 art and practice of the subject is scarcely more 



than fifteen years old. Leaving out of account 

 the large number of original memoirs on the scien- 

 tific side, we can say that broadly speaking the 

 books written on the subject fall into three groups. 

 There are first a few which deal in an advanced 

 manner with the scientific exposition of it, making 

 free use of whatever mathematical analysis may be 

 required, and assuming on the part of the reader 

 a sufficient preliminary acquaintance with physics. 

 Then at the other end of the bookshelf we find a 

 large number of smaller books which aim chiefly 

 at imparting to the amateur or practical operator 

 a knowledge of the use of the appliances and 

 instructions for making or operating wireless tele- 

 graph apparatus. An intermediate group of books 

 comprises the student's text-books, which, whilst 

 giving descriptions of apparatus, endeavour to 

 impart a certain degree of explanation of its opera- 

 tion suited to those whose acquaintance with 

 mathematics or physics is limited. The two books 

 before us belong to the latter class. 



(i) Prof. Rupert Stanley's book is marked by a 

 certain novelty of treatment and originality in 

 illustrations. He has not been content merely to 

 appropriate diagrams which have done duty 

 already in other books, but has prepared with con- 

 siderable care diagrams of circuits and schemes 

 of connections of apparatus in which the nature 

 of the magnetic and electric fields is clearly 

 denoted. This feature is of distinct assistance to 

 the student coming to the subject for the first 

 time. Also he has judiciously abandoned the usual 

 practice of describing wireless apparatus arranged 

 under various " systems " ascribed to particular 

 inventors, and has grouped the information in 

 chapters comprising descriptions of particular 

 elements in the apparatus. 



The first seven chapters of the book are devoted 

 to an exposition of the elements of electrical and 

 electrical engineering knowledge, to which, how- 

 ever, utility is imparted by basing it on the elec- 

 tronic theory. There is no doubt that this method 

 is a useful one. The student is in this manner 

 enabled to visualise some of the operations 

 better, but the teacher should at the same time 

 be careful to point out that there can be no finality 

 in any of our explanations of Nature's processes. 

 Because we can conceive a mechanism by which 

 the effects we see are brought about it does not 

 in the least degree follow that they are actually 

 done in that manner. A commendable feature of 

 the book is a series of questions at the end of 

 each chapter which will aid the teacher in testing 

 the results of his teaching. 



Some of the explanations in the book might 

 with advantage have been amplified. For in- 

 stance, in the description of Goldschmidt's high- 

 frequency alternator no explanation is given of the 



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