August 20, 1896] 



NA TURE 



36^ 



The Plague is treated by Dr. Payne. The bacteriology 

 of the disease, in the light of Yersin and Kitasato's 

 researches, is fully discussed, and the possibility of treat- 

 ment by antitoxine (Calmette). Relapsing Fever is dealt 

 with by Dr. Rabagliati ; the bacteriology of the subject 

 being from the pen of Dr. Westbrook. With this last 

 article \'olume i. closes. At the end of each monograph 

 there is a list of references, which are paragraphed, 

 according to the sub-section of the article to which they 

 refer. An accurate and extensive index of authors and 

 subjects greatly facilitates the use of the book. 



An idea of the labour requisite to the successful edit- 

 ing of a work like the one before us can only be formed 

 by the experienced few who have accomplished it. To 

 Prof Allbutt are due the thanks and congratulations of 

 cosmopolitan Medicine for having produced a work 

 which in fulness, accuracy and interest, leaves nothing 

 to be desired. F. W. T. 



A TEXT-BOOK OF EXPERIMENTAL 

 PHYSICS. 

 Lchrhiich tier Experimental PJiysik. Von Eduard 

 Riecke. Erster Band. Mechanik, Akustik, Optik. 

 Pp. xvi -t- 418. (Leipzig: Verlag von Yeit and Co., 

 1896.) 



I"' HE author, who is Professor of Physics in the 

 University of Gottingen, is well and favourably 

 known for his work in several departments' of physical 

 science, and the text-book he has written possesses the 

 qualities we should expect to find in the work of one 

 who is actively engaged not only in teaching physics, 

 but in advancing the subject by research. 



After an introduction on physical phenomena, physical 

 hypotheses and theories, and elementary measurements 

 such as those of angle, length, mass, and time, the 

 treatise enters on the subjects of mechanics and acoustics, 

 to which the first part of the present volume is devoted. 

 This occupies pp. 20-261, leaving pp. 262-418 for the 

 discussion of optics. 



In opening his dynamical treatment, the author does 

 not attempt to deal with the vexed questions of the 

 foundations of dynamics, a procedure which is perhaps 

 the best in the interests of beginners. The thoughtful 

 student will be confronted with the fundamental difficul- 

 ties soon enough, and according to his own ability and 

 the skill of his dynamical adviser will be his relief from 

 the serious mental embarrassment which he will inevit- 

 ably experience. The thoughtless student need not be 

 considered. 



The author postpones the consideration of mass, and 

 defines the unit of weight as the weight of a cubic centi- 

 metre of distilled water at maximum density under 

 atmospheric pressure, which he calls a grainme-gewichl. 

 We differ from the author as to this being the definition 

 of the unit of weight in the metric system. Surely that 

 unit is the weight of the standard kilogramme itself, or 

 of YoVii psrt of it. By the statement given the unit of 

 weight is not immediately connected with the standard 

 piece of matter ; though it is no doubt very nearly xS\n> of 

 the weight of the standard kilogramme. The unit of 

 NO. 1399, VOL. 54] 



weight is, however, made the weight of a unit of mass,. 

 and is therefore, strictly speaking, a variable unit ; it is 

 used throughout the treatment of the statics of rigid 

 bodies, with which the dynamical portion of the book 

 begins. 



The method adopted thus differs from that now usually 

 followed, in English books at least, by considering a 

 vertical string or bar which supports a body as stretched 

 by a force equal to the weight of the body, as measured 

 by the number of cubic centimetres of distilled water at 

 maximum density which will just equilibrate the body 

 in an accurate balance. Thus, so far as statics is con- 

 cerned, a preliminary kinetic definition and discussion of 

 force and the laws of motion are dispensed with. 



Whatever opinion may be held as to the merits or 

 demerits of this mode of presenting the subject of statics,, 

 there can be no question of the importance of referring 

 the student on every possible occasion for illustration 

 of principles and theorems to the great practical appli- 

 cations of dynamics that we have in abundance in 

 engineering structures, and of the use where possible of 

 graphical methods. This is an aim which the author 

 keeps well in view, though in order to proceed to the 

 consideration of stretching force and thrust, and ties and 

 struts, it does seem a little hasty to dismiss the parallelo- 

 gram of forces with a mere experimental proof by means 

 of strings and weights. 



The discussion of the kinetics {dynamics the author 

 calls it) of solid bodies follows. This has many points of 

 excellence. But we must rather demur to the comparison 

 of the absolute and technical units, given at p. 67. Thus 

 it is stated — 



Absolute. 

 Unit of mass equal to the 

 mass of a gramme. 



Technical. 

 Unit of force equal to the 

 weight of a gramme at latitude 



45°- 



Unit of force equal to the Unit of mass equal to the 



weight of -551 gramme at lati- mass of 9S1 gramme weights, 

 tude 45°. 



Whatever the somewhat disputed relative merits for 

 different purposes of the absolute and technical system 

 of units may be, it is universally admitted that the 

 absolute C.G.S. unit of force is that force which gives a 

 mass of one gramme an acceleration of i centimetre per 

 second per second. To define it, or state its value as 

 above, is to give no doubt a constant unit of force (on 

 the supposition that gravity is constant at latitude 45°), 

 but one differing perceptibly from that usually defined as 

 the absolute unit, smce the value of g at latitude 45° at 

 mean sea-level is approximately 980-61 in centimetre 

 second units. The great beauty of the absolute system 

 as given by Gauss, surely lies in the fact that the funda- 

 mental units of length, mass, and time do all for us, and 

 we have, so far as the definition of dynamical units is 

 concerned, nothing whatever to do with gravity. 



The proper definition of the unit of force it must be 

 stated, however, is given belo^v this " Gegemiberstellung" 

 of units, so that the author probably does not offer the 

 statement in the table as other than a comparison of 

 values of units ; but it is well to give first the definition, 

 and rub it in with plenty of illustration. Only after the 

 student has become perfectly familiar with the system of 



