C. GENERAL PHYSICS. 143 



and theoretical, into the various methods of measuring very- 

 high temperatures, by Professor Weinhold, with the assistance 

 of Dr. Schreiber, who was a student at the time the observa- 

 tions were made. The methods considered in the course of 

 this investisration included the foUowins; : 



First, the exj^ansion of volume ; second, the variation, in 

 pressure, of inclosed gases, or the two forms of the air thermom- 

 eter ; third, the warming of a cold mass of any substance 

 by heat, or the calorimetric methods; fourth, the melting of 

 hard bodies; fifth, the conduction and radiation of heat ; 

 sixth, the change in the velocity of sound ; seventh, the efiect 

 of heat on optical phenomena; eighth, the dissociation of 

 chemical compounds ; ninth, the development of electricity 

 by the thermo-electric method ; tenth, the change of the co- 

 efficient of electric conductivity. 



Some of these, indeed, needed but a few passing remarks 

 to dispose of their claims to accuracy. Of them all, the first 

 method, that of the air thermometer, although most difiicult 

 of application, is theoretically adapted to give standard re- 

 sults ; and the object of the author has been to ascertain 

 whether some other method can not be found that, in com- 

 parison with this, shall be sufiiciently accurate and much 

 more convenient. After detailing the various precautions 

 taken to prepare an air thermometer whose results should be 

 of the highest attainable reliability, the author explains that 

 the construction of the apparatus which he employed was, 

 with some modifications, the same as that used by Kegnault, 

 Magnus, etc., and consists in measuring the pressure of a de- 

 finite mass of air whose volume is kept approximately con- 

 stant. The determination of the boiling-point of pure zinc, 

 at 1035 Centigrade (1895 Fahr.), he considers to be the 

 most accurate that has yet been made, and with as perfect a 

 standard as this Professor Weinhold then proceeds to com- 

 pare the various pyrometers of Gauntlets, Bock, and Oechsle, 

 and shows them to be quite unreliable within the demands 

 of modern science, even for temperatures of' 500 and less. 

 He next investigates the expansion of metals and liai'd bodies, 

 as glass, porcelain, quartz, etc., and shows that all these bod- 

 ies have such irregularities in their rates of expansion as to 

 be practically worthless. The specific heat of a body at low 

 temperature is not the same as that at a higher temperature ; 



