'')10 'Notices respecting New Books. 



" 772 on the Fahrenheit scale " ; Mayer is credited with an experi- 

 ment which was repeated by Joule, whose object in experimenting 

 is rather made to appear as the justification of Mayer's hypothesis. 

 Technical terms, too, are used without definition : thus the idea of 

 ifficiency is introduced on p. 26 without any explanation though 

 its quantitative measurement is concerned, and, indeed, when an 

 implicit definition is finally given on p. 35 in connexion with a 

 Carnot cycle, it is in terms which are neither general nor such as 

 Carnot could have accepted. It may also be pointed out that 

 in Chaps. XVI. and XVII. there is no distinguishing symbol for 

 absolute temperature, though everywhere else the letter r is used ; 

 that in Chapter XT. the numerical specification of entropy diners 

 from that adopted elsewhere ; and that in (151) only a particular 

 integral is given of the partial differential equation (150), the 

 general solution of which is K=r 2 /(r 3 — 3At 2 jj) corresponding to 

 the characteristic tyr=;£(£>)-|-Ar f<:Zr r — 2 /(- 3 — SAr^). 



The notation is not all that can be desired; that of partial 

 differential coefficients is specially abused, after Clausius' example, 

 in being applied to denote thermal capacities, and in Chap. XI. 

 the differential coefficients of p and X with respect to t are con- 

 tinually enclosed in brackets armed with some such subscript as 0, 

 which is entirely incorrect, as these are not partial differential 

 coefficients at all except with respect to the state of saturation ; 

 elsewhere, too, occurs repeatedly the meaningless form (dr/dt)^, 

 wherein t is an acknowledged function of t only. 



These are, however, blemishes which do not impair the value of 

 the book, but might be considered in view of a second edition. 

 Among its good points must specially be mentioned the stress that 

 is laid on the proper definition of absolute temperature, though 

 on p. 168 the author himself uses the definition to which he objects ; 

 and there is an interesting modification of Eankine's characteristic 

 for gases suggested which deserves discussion. It is further well 

 remarked that even on the caloric theory Clapeyron's version of 

 Carnot's operations (which is that adopted in the book) would be 

 improved by the adoption of Clausius' modification, — which, by the 

 way, is ascribed to J. Thomson, though contained in that memoir 

 of Clausius which first set the subject on its new basis. It may 

 be here remarked that Carnot's own version of his cycle requires 

 no modification whatever, even from the new point of view. 



Die pliysiTcalische Behandlung und die Messung holier Temperatures. 

 By Dr. Carl Baetjs. Leipzig : Barth, 1892. 



The subject of pyrometry, although forming an important 

 application of physics to manufactures, has not received from 

 physicists the attention which it deserves. One reason for this is 

 undoubtedly the difficulty of maintaining a constant high tempera- 

 ture, and another is to be found in the fact that the subject neces- 

 sitates a detailed study of the alterations produced in the properties 

 of matter by excessive heating. In order to measure any tempera- 



