144 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



and the imperfection of our knowledge of the rate at which 

 specific heat changes leads Weinhold, before investigating 

 the value of the calorimetric pyrometers, to first study the 

 change of specific heat at temperatures of 900, and less, for 

 platinum and for iron. The latter proves to be far the better 

 of the two metals for the purpose in view, and tlie errors of 

 the result are not too large to forbid the use of iron in the 

 calorimetric method. The specific heat of platinum varies, 

 with curious irregularities; while for ii'on the changes are ap- 

 parently very regular. The very promising method of Lamy, 

 or the dissociation thermometer, does not give satisfactory 

 results, though the author proposes to continue his researches 

 in this direction. Finally, Weinhold tests the Siemens' py- 

 rometer, whose principle of action is the measure of the in- 

 crease in the resistance offered by a heated wire to the pas- 

 sage of a galvanic current. Tlie instrument employed by 

 him had been constructed for use in temperatures of less 

 than 500, and for such was found perfectly trustworthy. 

 For temperatures up to 1000 its error was small and nearly 

 constant, so that this method was decided to be the best of 

 all that were examined. Weinhold thus sums up his results, 

 which are of interest to all enoracred in those manufactures 

 requiring tlie use of higli temperatures : 



First. Of all the pyrometers that are sold ready for im- 

 mediate use, the Siemens' only is to be recommended. 



Second. The calorimetric method, used in a proper way, 

 can serve as a pyrometer. Programme tech. Schnle^ Chem- 

 nitz. 



TENSION OF VAPORS FROM SOLIDS AND LIQUIDS. 



A result of much practical interest in the study of the 

 theory of hygrometry has been announced by Montier, who 

 establishes the interesting point that any body emits a vapor 

 having a tension depending not only on the temperature, but 

 also on the physical condition of the body; for instance, the 

 vapor of water at 32, and of ice at 32 Fahr. The demon- 

 stration of this principle involves the truth of the dynamical 

 tlieory of heat, which seems to establisli the fact that if a 

 body can exist at the same temperature, yet in two different 

 states, characterized by a difference in the respective coeffi- 

 cient of specific heat, then the vapors emitted by the body in 



