166 Dr. H. F. Weber on the Specific Heat of 



Perfectly analogous results were obtained for graphite in two 

 series of researches. From experiments made in the autumn of 

 1872, I concluded that the specific heat of crystalline boron in- 

 creases with the temperature exactly as that of diamond and 

 graphite increases, and that, at any rate for low temperatures, 

 the specific heat of silicon varies with the temperature. Follow- 

 ing up these preliminary researches, I have now for two years 

 busied myself with an inquiry into the relation subsisting between 

 the specific heats of the various modifications of carbon, silicon, 

 and boron, and the temperature at which these are determined. 

 As the investigation advanced I found that comprehensive de- 

 terminations of the specific heat of these elements, as a function 

 of the temperature, might lead to a removal of the idea that these 

 bodies form an exception to the law of Dulong and Petit, and also 

 to a new point of view from which to regard this law itself — that 

 these numbers might also be useful in further determinations of 

 the specific heat of the various modifications of any element, or 

 of the specific heats of the elements when in chemical combina- 

 tion. I therefore spared no trouble in obtaining exact and trust- 

 worthy determinations of the specific heats of these elements at 

 as many and as various temperatures as possible. Over a hundred 

 careful measurements have been made. As regards-carbon in 

 the free state, all the problems which presented themselves have 

 been solved ; the specific heat of the different carbon-modifica- 

 tions has been determined for all temperatures between — 80° and 

 ■4- 1000°. Only in connexion with the elements boron and silicon 

 a few questions yet remain unanswered. I prefer, however, to 

 publish the results which I have obtained ; and in the next Part 

 I hope to correct any errors and to extend the investigation. 



The greater part of this research was carried out in the Phy- 

 sical Institute of the University of Berlin, between December 

 1872 and July 1873, the remainder being conducted in the pre- 

 sent year at Hohenheim and Stuttgart. (The author expresses 

 his thanks to Professors Helmholtz, Rammelsberg, and G. Rose 

 of Berlin, Tschermack of Vienna, and Marx of Stuttgart.) 



I. Methods of Observation. 



Let Wj, W 2 , . . . W„ be the amounts of heat which G weight- 

 units of a body give up when cooled from the initial temperature 

 T lf Tg, . . . T n to the final temperature T in a calorimeter ; n dif- 

 ferent values for the specific heat of the body y T in relation to 



the temperatures -^ — -> -^ — l , . . . n n ~ * may be deduced 



(and hence what function of the temperature the specific heat 

 represents), provided that the temperature-differences T^ T , 



