September 30, 1920] 



NATURE 



143 



\ 



present edition to make a number of changes, 

 some of which call for brief comment. 



The tables dealing with the relative accelera- 

 tions due to gravity at different latitudes have 

 been recomputed on the basis of the recent work 

 of the L'.S. Coast and Geodetic Survey. New 

 water-vapour pressure tables have been recalcu- 

 lated from the latest Reichsanstalt investigations, 

 a modification of V'an der Waal's formula being 

 employed for the purpose of interpolation. 



These alterations have involved extensive re- 

 vision of a number of associated barometric 

 tables, together with those dealing with the ven- 

 tilated hygrometer, the treatment of which is very 

 satisfactory. The most important advance in the 

 matter of the wet- and dry-bulb hygrometer was 

 the discovery (known to Belli so far back as 

 1830) that it may be made a trustworthy instru- 

 ment if the wet bulb is exposed to moving instead 

 of to still air. Even then different instruments 

 were found to give different readings to an extent 

 depending i)n the shape and dimensions of the 

 thermometer bulb and stem. 



But all such idiosyncrasies were swept away 

 by the later discovery that if an air-velocity of 

 not less than 3 metres per second is employed, 

 agreement results in the readings afforded by 

 various instruments. In practice the velocity of 

 the air need not be known so long as it is above 

 that which gives sensibly the greatest depression 

 of the wet-bulb thermometer. 



Among other new tables are those for convert- 

 ing barometric inches or millimetres of mercury 

 into the millibars which now receive international 

 acceptance. 



The various logarithmic and simpler trigono- 

 metrical tables which appeared in former editions 

 have now been omitted — a retrograde step, we 

 think, from the point of view of the convenience 

 of the reader. 



It may not be known to ail readers of Nature 

 that the Smithsonian tables are not obtainable in 

 the ordinary way by purchase through a book- 

 seller. 



Our Bookshelf. 



Elements of Radiotelcgraphy. By Lieut. Kllery VV. 

 Stone, L'..S. N.R.F. Pp. vii -(- 267-1- xxxiii plates. 

 (London : Crosby Ix>ckwood and Son, 1920.) 

 Price i6j. 6<i. net. 



This is a work written with the primary object 

 of forming a manual of instruction for those in 

 the wireless branch of the L'.S. Navy, but on 

 account of the clear sketch of the subject it gives, 

 it will probably appeal to a wider rirt !«•. The way 



NO. 2657. VOL. 106] 



in which the elementary principles are set forth 

 should be appreciated on both sides of the Atlantic. 

 Details are given of several systems better known 

 in .\merica than here, but French and German 

 methods, as well as some originating from this 

 country, are also dealt with. The book has a 

 breadth of outlook which is refreshing after some 

 works which tend towards making one think that 

 all wireless progress is due to one group of investi- 

 gators. The author does not favour any one 

 system unduly, although naturally he has to base 

 a certain proportion of his remarks upon the 

 various systems employed in the American Fleet. 

 This includes a good deal of interest regarding 

 the recent developments of the Poulsen arc system, 

 and apparatus up to 1000 kw. is illustrated. 

 We only regret that considerations of space have 

 rather curtailed the treatment of the thermo-ionic 

 valve, or "electron tube," and that wireless tele- 

 phony, as distinct from telegraphy, receives only a 

 passing reference, for it is well known that the 

 American Navy made early advances in this direc- 

 tion. The treatment throughout is non-mathe- 

 matical ; the range covered embraces elementary 

 principles as well as up-to-date methods, and the 

 illustrations are excellent 



Exercises from Elementary Algebra. By C. 

 Godfrey and A. W. Siddons. Vols. i. and ii., 

 complete. ( W^ith Answers). Pp. x -I- 395-1-0. 

 (Cambridge : At the University Press, 1920.) 

 Price 7s. 6d. net. 



The exercises in this book are identical with those 

 in the first edition of "Elementary Algebra " by 

 the same authors, with the exception that some 

 new revision papers have been inserted. The first 

 fourteen chapters deal with elementary algebra up 

 to quadratic equations, graphs, and the graphical 

 solution of equations of degree higher than the 

 second. Then follow thirteen chapters which take 

 in logarithms, surds, progressions, rate of change 

 and simple differentiation and integration. An 

 appendix of eight chapters on various forms of 

 linear and quadratic equations, on factors, etc., 

 has l)een added. 



Catalysis and its Industrial Applications. By E. 

 Jobling. Second edition. (Text-books of 

 Chemical Research and Engineering.) Pp. viii-f 

 144. (London : J. and A. Churchill, 1920.) 

 Price 7s. ttd. net. 



The first edition of this useful little book was 

 reviewed in Nati re for February 17, 1916. Since 

 that time, the subject of catalysis has undergone 

 extensive developments, and the present edition 

 aims at bringing the book up to date. Besides 

 necessary alterations, two chapters have been 

 added, one on the synthesis of acetic acid, alcohol, 

 and allied compounds, and the other on enzymes, 

 electro-chemistry, and vulcanisation accelerators. 

 A number of references, both to textbooks and to 

 patents, are given at the end of each chapter for 

 the assistance of readers desirous of obtaining 

 fuller details of the processes discussed. 



