3o6 



NATURE 



[November 4, 1920 



114-8 million bushels. This astonishing change is 

 a remarkable achievement for which the Allies may 

 well be grateful and of which America may justly 

 be proud. The total production of food natur- 

 ally did not increase to the same extent. The data 

 are : — 



Total Food Production in the United States : 

 Metric Tons, Millions. 



Total 



Calories, 



Total Carbo- million 



food Protein Fat hydrates millions 



Average for 7 years, 191 1-18 QO'2 41 57 l6'3 137'2 



„ 3 prewar years 850 38 15-5 15-3 129 3 



„ warpeiiod .. 937 4-2 59 17-1 143° 



Animals contributed 58 per cent, of the total 

 food, 50 per cent, of the protein, and 83 per cent. 

 of the fat. 



The table further shows what a vast amount of 

 food has to be grown in order to produce a suflfi- 

 ciency of nutrients; only 29 per cent, of the total 

 tonnage of human food is net nutrients ; the re- 

 mainder is water, ash, and inedible refuse. 



Comparing the annual increases in the pro- 

 duction of food with the growth of the population, 

 Prof. Pearl arrives at the comforting conclusion 

 that the food supplies of the United States are 

 increasing more rapidly than the population, so 

 that there is "as yet no occasion for worry along 

 Malthusian lines in this country so far as sub- 

 sistence is concerned." 



Study of the details of Prof. Pearl's tables brings 

 out a number of points of importance to adminis- 

 trators. The very small part played — and play- 

 able—by the so-called " home garden " movement 

 is shown by the fact that the total vegetable pro- 

 duction of farm and garden amounts to only 2 per 

 cent, of the total Calorie production in human food, 

 and of thrs 2 per cent, a large proportion is coii- 

 tributed by commercial concerns. Similarly, 

 poultry contributes less than 2 per cent, of the 

 Calories. Cows, pigs, and wheat are the great 

 reservoirs, contributing together 62 per cent, of 

 all the protein and carbohydrate used as human 

 food, 69 per cent, of all the fat, and 65 per cent. 

 of all the Calories. Obviously, if there is to be 

 an increase in human food we must concentrate 

 on these (and in England on the sheep as well), 

 and not lose ourselves in less important items, 

 although, on the other hand, we must not fail to 

 develop even a i per cent. item. 



The distribution of this enormous production is 

 elaborately dealt with. The high-water mark of 

 exports was reached in the year 1914-15; there- 

 after they fell, and in 1917-18 were down almost 

 to pre-war level ; but, of course, the exported 

 food was all going to the Allies instead of being 

 distributed over the world. The 1914-15 result is 

 NO. 2662, VOL. 106] 



explained by supposing that all reserves were then 

 cleared out — a process obviously possible once 

 only. In spite of the high exports, more food 

 remained in the United States than in the pre- 

 war period, which may be connected with the 

 larger and more prosperous domestic population. 



Finally, a table is given showing the average 

 daily consumption per "adult man." For conveni- 

 ence the British data are also given. The figures 

 are as follows : — 



Calories 



3424 



4288 



4009 



3400 



The United Kingdom figures are taken from the 

 Royal Society's Report (Cd. 8421), and show that 

 we eat less than our cousins across the water, 

 unless, indeed, we waste less. 



E. J. Russell. 



Theory of Electric Cables. 



The Theory of Electric Cables and Networks. 

 By Dr. Alexander Russell. Second edition. 

 Pp. x-f348. (London: Constable and Co., Ltd.. 

 1920.) Price 245. net. 



DR. RUSSELL'S weJl-known book on the 

 theory of electric cables and networks is 

 one which should be increasingly studied as the 

 complex networks, which are now required in con- 

 nection with large power stations, are constructed. 

 The book is already well known to electrical 

 engineers. It lays down those fundamental prin- 

 ciples on which all designs of cable networks must 

 be built up. The kilowatt capacity of central 

 stations for generating electrical Energy is now 

 three times as large as it was when the first 

 edition of Dr. Russell's book was published, and 

 the importance of economical design in cables and 

 networks is much more clearly recognised than it 

 was twelve years ago. 



The chief difference between the first edition 

 and the second is the introduction of new chapters 

 on alternating current theory and systems of 

 supply, and in the inclusion of numerical examples 

 which will make the book more useful for begin- 

 ners. Some further extensions of Kelvin's law 

 have been made, and an account is given of recent 

 developments in cable construction. The scope of 

 the work is so well known that it is not necessary 

 to review it in detail. It deals with the proper- 

 ties of conductors and of insiJating materials, 

 methods of testing them, and the economy of the 



