June 25, 1903] 



Ir 



^^B Physical Laboratory of Christiania, and during 

 ^^Blast two years Mr. S. Svendsen assisted in the work. 

 ^^But 1880, Prof. C. A. Bjerknes received from the 

 ^^Brwegian Government a private laboratory, where 

 ^H^ experiments were arranged by the author with the 

 IRssistance of Mr. J. L. Andersen. The result of these 

 facilities was the construction of an elaborate instru- 

 ment for measuring the attractions and repulsions of 

 bodies pulsating in liquid. The generator consists of 

 a system of pumps or drums operated on as bellows by 

 cranks worked by a handle. These alternately force 

 air in and out of the " pulsators," which may consist 

 I ither of elastic balls, drums, or similar arrangements 

 >uspended in the water by a " pulsation balance," and 

 tlie whole apparatus is now supplied by Ferdinand 

 Ernccke, of Berlin. Another form of apparatus is 

 described suitable for studying bodies oscillating in 

 Aater without change of volume. Methods are also 

 described of rendering the stream lines visible, and 

 diagrams are shown illustrating the resemblance of 

 these lines to magnetic lines of force. 



The description of the experiments occupies the 

 second part of the book. The first part consists of a 

 summary of the main results, both quantitative and 

 qualitative, which were established in vol. i., treated 

 by elementary methods only, and it serves the purpose 

 of enabling the physicist to read the present volume 

 without studying its more mathematical predecessor. 

 F'or such a reader the third part will have consider- 

 able interest, for it deals with the analogy of hydro- 

 dynamical phenomena with those of electrostatics and 

 magnetism. Prof. C. A. Bjerknes 's original discus- 

 sions of these analogies having been given at a transi- 

 tion period in the development of electrical science, the 

 writer of the present volume has largely remodelled 

 the arguments in order that they may be studied in the 

 light of modern electrical views. Between hydro- 

 dynamical and electric or magnetic fields of force, a 

 close analogy exists except in regard to the sign of 

 the force. The stream lines due to spheres executing 

 pulsations of the same phase are identical with the 

 lines of force due to like charges, but the pulsating 

 spheres attract one another while the electrified 

 spheres repel one another. If the pulsations are of 

 opposite phases, the stream lines are the same as the 

 lines of force of oppositely charged bodies, but the 

 force is repulsive instead of attractive. Owing to this 

 difference, the hydrodynamical field is to be regarded 

 as affording a representation rather than an explan- 

 ation of electric and magnetic fields, and as Prof. V. 

 Bjerknes points out, a negative representation is still 

 a representation, and it may admit of all the uses of a 

 positive one. 



Prof. V. Bjerknes has uniformly adopted the Heavi- 

 side system of " rational " electrical units, and he 

 points out the great simplifications that arise from the 

 use of this system, expressing his regret that the exist- 

 ing units were adopted before the advantages of the 

 rational system had been fully appreciated. 



The book will be read with much interest by 

 physicists, and the reproduction of some of the experi- 

 ments in the lecture room suggests a useful aid to the 

 teaching of electricity. G. H. Brvan. 



NO. 1756, VOI-. 68] 



NATURE 



^n 



FARM ACCOUNTS. 

 The Farmer's Business Handbook. By I. P. Roberts. 

 Rural Science Series. Pp. xiii + 300. (New York : 

 The Macmillan Company ; London : Macmillan and 

 Co., Ltd., 1903.) Price 4s. 6J. net. 



THIS volume of the Rural Science Series consists 

 firstly of an elementary account of book-keeping 

 suitable to a small farm, and secondly a discussion of 

 such legal questions as leases, tenant right, highways,, 

 fences, mortgages, taxes, &c., with which an ordinary 

 farmer is likely to become conveisant in the course 

 of his business. This latter portion of the book is. 

 naturally only applicable to the United States, and 

 though succinctly and clearly written, can be of little 

 service to the English reader. In the earlier section 

 of the book a system of book-keeping is set out by 

 which the farmer can ascertain not only his profit or 

 loss as a whole, but the result of his operations on each 

 field or in each section of his business. The usual 

 method of double entry is employed, though only day 

 book (for which the American equivalent is apparently 

 " blotter ") and ledger are kept. The explanations are 

 clear and simple, and may be read with profit by 

 students who are beginning formal book-keeping, and 

 are getting confused over the problem of Dr. and Cr. 

 But we are by no means convinced that the ordinary 

 system of double entry is the best method of handling 

 farm accounts; naturally it can be made to deal with 

 them, and for the cash account nothing different is 

 wanted, but it is an extremely cumbrous means of 

 ascertaining the profit or loss on individual crops or 

 classes of live stock. Farmers are often reproached, 

 and justly enough, with not keeping proper accounts, 

 but it is not quite so easy a matter as in a business 

 where all the items are in sight. So many of the 

 figures must be estimates depending upon the judg- 

 ment of the farmer ; first of all the annual stock-taking 

 has to be a valuation, in which market fluctuations 

 have, or have not, to be considered, according to the 

 purpose of the account. For example, a man has a 

 breeding flock the number of which remains constant ; 

 in ascertaining his profits upon sheep-breeding it is 

 best to take the value of the flock as constant, but in 

 ascertaining his financial position at a given moment,, 

 he must re-value the flock at current rates. Again,, 

 many operations upon a farm are performed as much 

 for their contingent advantages as for immediate re- 

 turn ; the dung and cultivations given to the root cropi- 

 have their value throughout the rest of the rotation ; 

 cattle are fattened for the sake of the manure they 

 produce. 



To one point the author of this book very properly 

 gives special prominence, the item of household ex- 

 penses; the house rent, the milk, potatoes, &c., con- 

 sumed, the labour spent, are very otten not taken into 

 account at all, and the farmer sometimes comes to the 

 conclusion that his farm is not paying when he is 

 really living beyond his income. On the whole we 

 believe that the ideal system is to open a ledger account 

 for all cash transactions and for the house, and tQ. 

 keep separate running or progress accounts against 

 the main branches of his business, such as the dairy 



