Dr. H. F. Weber on the Specific Heat of Carbon. 251 



in any desired position. The screw S serves to regulate the ra- 

 pidity of the exhaustion_, or^ in cases of simple aspiration, the 

 amount of air passing through the holes in the cone. S' is a 

 clamping arrangement^ by which the vacuum within the pump 

 can be maintained without disturbing the screw S if it should be 

 necessary suddenly to disconnect the caoutchouc tube J) from 

 the vessel to be exhausted. 



This brief account of the slight but serviceable modifications 

 in the original instrument of M. Jogno is made with the object 

 of introducing an exceedingly valuable piece of laboratory appa- 

 ratus to a more extended notice than it has hitherto met vv'ith in 

 this country. 



XXXI. On the Specific Heat of Carbon. By H. F. Weber, 



Assistant in the Physical Laboratory o/Geh.-R. llelmholtz.* 



To the Editors of the Philosophical Magazine and Journal, 

 Gentle ME Nj Berhn, 25th Aug. 1872. 



IN yesterday^s Number of the ^Athenaeum/ 24th August, 

 p. 238, I find the following :— 



"British Association. Section B. Chemical Science. 



" Mr. Dewar made a communication ' On the Specific Heat of 

 Bodies at high temperatures, with particular reference to that of 

 Carbon/ which he showed, from the results of a very carefully 

 conducted series of experiments, increased in a very rapid man- 

 ner with the increment of temperature. His observations were 

 made at the temperature of boihng zinc, and of the oxyhydrogen 

 blowpipe &c.-'^ 



This property of carbon, however, I had previously discovered, 

 and laid a detailed memoir on the subject before the Physical 

 and Chemical Society of Berlin. An abstract of that memoir 

 was published in the Berichte der deutschen chemischen Gesellschoft 

 in April of this year. The latter seems to have escaped the 

 notice of the Chemical Section of the British Association. As 

 from this it appears that the Berichte are not so widely circu- 

 lated in England as we in Germany think, I request you to print 

 the enclosed brief memoir and this letter in the next Number of 

 your valued Journal. 



Your most obedient. 



Dr. Friedrich Weber. 



In 1819 Dulong and Petit deduced, from the investigation of 



* Translated from a separate copy communicated by the Author, from 

 the Berichte der deutschen chem. Gescllsch. zu Berlin, having been read 

 bv the Author at the Meeting on the 24th of March, and at the Physical 

 Society on the 21st of March, 1872. 



