NATURE 



[March 2, 1916 



previous large number. Statics occupy the first 

 eight chapters, then follow three chapters on 

 motion, two chapters on work and friction, a 

 chapter on the dynamics of rigid bodies, and 

 another on impacts. 



The book differs somewhat from most of the 

 text-books on applied mechanics for engineers 

 produced in this country ; had it been published in 

 Great Britain it would probably have been called 

 "Applied Mathematics for Engineers." The 

 treatment of the principles of mechanics is excep- 

 tionally good, and we can confidently commend 

 the book to any engineering student who wishes 

 to understand more thoroughly many matters 

 which receive but little attention in most of our 

 own text-books. With the omission of some of 

 the more mathematical sections, which could be 

 read profitably by engineering students later in 

 their course, the book would prove very useful to 

 students who desire to attain the standard of the 

 intermediate examinations of the universities. 

 There is a capital section on moments and pro- 

 ducts of inertia, containing matter for which the 

 engineering student has generally to search in 

 books containing little else of interest to him ; the 

 practical examples given in this section are good. 



The British Journal Photographic Almanac and 

 Photographer's Daily Companion, 1916. Edited 

 by G. E. Brown. 55th issue. (London : H. 

 Greenwood and Co., Ltd.) Price is. net. 

 All those who are practically interested In photo- 

 graphy look forward to the appearance of the 

 "B. J. Almanac," and in spite of the stress of 

 circumstances they will not be disappointed. 

 Although there are fewer new things to chronicle 

 for last year, the general features of the volume 

 are much as usual. The editor's special contri- 

 bution is a long article on printing processes. 

 These " practical notes " will be much appreciated. 

 The " Epitome of Progress " section preserves its 

 usual character, but the section usually devoted 

 to a review of the novelties introduced by the trade 

 during the past year is replaced by a survey of 

 the resources of Great Britain and certain well- 

 known firms of Entente nationality in the produc- 

 tion of the requisites for photography. This 

 shows that in several important respects we are 

 rendering ourselves independent of German 

 supplies. 



An Introductory Course of Practical Magnetism 

 and Electricity. By Dr. J. R. Ashworth. Third 

 Edition. Pp. xvii + 96. (London : Whittaker 

 and Co., 191 5.) Price 2s. net. 

 The laboratory course described in this book is 

 divided into thirty sections, and can be worked 

 through in the course of a winter session. The 

 present edition of the book is substantially the 

 same as the previous issues, though some addi- 

 tions have been made. Sections have been intro- 

 duced on the measurement of the internal resis- 

 tance of a cell and the effect of joining cells in 

 series and in parallel, and upon the use of the 

 Wheatstone bridge for the comparison of 

 resistances. 



NO. 2418, VOL. 97] 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible fur 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or a)iy other part of Nature. No notice is 

 taken of anonymous communications.] 



Exploration in South-West Africa. 



Prof. H. H. VV. Pearson, of Cape Town, has just 

 conducted an exjiloring expedition through part of the 

 recently conquered "South-West." The expedition, 

 which is expected to yield important economic as well 

 as scientific results, started with the express approval 

 of General Botha, and, like Prof. Pearson's previous 

 journeys through the less explored parts of South 

 Africa, was promoted by the Percy-Sladen Memorial 

 Trust. I have just received the following letter, and 

 I am sure many readers of Nature will be glad to 

 learn from it that Prof. Pearson has returned safely 

 from his interesting and successful trek. 



W. A. Herdman. 



University of Liverpool, February 18. 



Cape Town, 



'January 28, 1916. 

 Dear Prof. Herdman, 



Just a line to tell you that the journey is accom- 

 plished with results which I hope will prove to be quite 

 successful. I learned just what I wanted to learn and 

 a good deal more besides. The route was a particu- 

 larly interesting one ; it showed me more of the transi- 

 tion zone between the littoral desert and the plateau 

 than I had expected, and it gave me a good insight 

 into the relations between the Damaraland and Nama- 

 qualand floras. It has connected up the results of 

 my previous journeys, and I can now tackle my 

 general summary much more satisfactorily than I 

 could have done before. 



The journey itself was in some respects the most 

 difficult I have ever done. Along the edge of the 

 desert the road disappeared entirely, and we got 

 entangled in the ravines of a peculiarly awkward 

 range of mountains. On December 31 we spent five 

 hours in advancing considerably less than a mile. 

 Both the wagons broke down, one of them twice 

 within half an hour and in a vital part. But for the 

 extraordinary skill of the two Hottentot drivers we 

 should never have got them both through. Darkness 

 found us in a dangerous river-bed, in which, in 

 defiance of all the laws of good trekking, we had 

 to spend the night — and a sleepless one so far as I 

 was concerned. However, the new year was kinder, 

 and although we broke down again in later stages 

 of the journey, I had the satisfaction of taking ever>'- 

 thing safelv into Windhook except two of my thirty 

 donkevs. One of these died on the road ; the other I 

 left in a weak condition with one of our military 

 outposts, and it eventually recovered. Our troubles 

 were due primarily to a bad mistake in the German 

 maps, and to the fact that for 120 miles the country 

 was absolutely without inhabitants, white or 

 black. . . . 



I passed through the semi-independent territory of 

 the Bastard Hottentots. No German dare venture 

 into it, but when these people found I was English 

 thev could not do enough for me. The chief sent his 

 son with me for thirty miles to make sure that I 

 regained the trunk ro'ad lost through the mistake 

 mentioned above. They and all the natives through- 

 out the countrv are profoundly thankful that the 

 German regime' is over— and they have good reason 

 to be H. H. W. Pearson. 



