REVIEWS 163 



interested from other points of view. The author's review of the general 

 economic condition leads him to believe that the comparative lack of un- 

 developed fertile regions, the increase in white meat-eating population, and 

 the general tendency for the consumption of meat per head to rise, will lead 

 to there being a shortage of animal foodstuffs and a rise in their cost in the 

 near future. He points out, however, that this shortage may be met in part 

 by an increased consumption of fish and dairy produce, and that it may be 

 followed within a decade by a period of comparative abundance, provided 

 favourable conditions present themselves. Turning to the conditions within 

 the British Empire, he shows that the deficiency tends to be even more 

 marked than when the world generally is considered, and that it can only 

 be remedied by a great increase in the labour and capital devoted to agri- 

 cultural production. Otherwise, we will inevitably become increasingly 

 dependent on foreign sources. 



This monograph is a valuable contribution to our knowledge of a most 

 important subject. 



J. C. D. 



Telephonic Transmission, Theoretical and Applied. By J. G. Hill, Assis- 

 tant Staff Engineer, General Post Office, London. [Pp. xvi -f- 398, 

 with 196 diagrams and illustrations.] (London : Longmans, Green & 

 Co., 1920. Price 21s. net.) 



The erection of a telephone circuit between any two places at the present 

 day resolves itself into much more than the mere provision of a pair of 

 connecting wires between the two instruments : it requires extensive pre- 

 liminary calculations to determine not only the sizes of wire and the form 

 of the circuit, but also to predetermine its speaking qualities. 



This book by Mr. J. G Hill, Assistant Staff Engineer, General Post Office, 

 London, treats of such design, not merely from the purely theoretical stand- 

 point of the propagation of the telephonic currents along the lines, but also 

 from the practical point of view which involves considerations of cost and 

 economy, and of the elements of standardisation which are so essential in a 

 large system, but which necessarily often introduce modifications into the 

 theoretically best solution of any given problem. The book therefore differs 

 considerably from others dealing with the theory of such transmission, and 

 its arrangement is consequently somewhat unusual. 



For instance, the author first deals with the case of direct current trans- 

 mission along an infinite line, and it is not until Chapter V that the essential 

 features of telephonic transmission — depending as it does upon the use of 

 alternating currents of many frequencies— are introduced. 



The author has endeavoured to dispense as far as possible with the use 

 of " higher mathematics " in the treatment of his subject, and thus to over- 

 come some of the mysteries of differential equations and similar functions, 

 and to substitute in their place a simpler treatment. This treatment, together 

 with the more classical method of developing the transmission formulae, the 

 author has relegated to appendices — an arrangement which, in the reviewer's 

 opinion, does not tend to enhance the clarity of the book, since one at least 

 of these appendices must be read in its place in the opening paragraphs of 

 Chapter II in order to obtain a connected account of the subject. 



In Chapters VI to IX the formulas particularly applicable to telephone 

 lines are developed in detail, and the method of calculating the various trans- 

 mission constants of such lines is given, while in Chapter IX some fifty-five 

 pages are devoted to the problems of loaded telephone lines particularly 

 with reference to British Post Office practice. Chapters X and XI cover 

 very important ground in describing various methods of measurement of 

 the constants of telephone lines, and the uses of Standard Cable in such 



