for Measuring the Expansions of Solids, 8fc. 

 Table X. 



351 



The most remarkable fact displayed by the preceding com- 

 parison is the beautiful accordance of the results obtained 

 from two metals whose expansions are so diiferent as those of 

 platinum and iron. The temperature indicated by the latter 

 exceeds that by the former in the instance of the fusing point 

 of gold 35°, and in that of silver only 29°; and this excess is 

 in accordance with the conclusion of MM. Dulong and Petit, 

 exhibited in Table II., that the expansion of iron increases 

 in the higher degrees in a greater proportion than that of 

 platinum. 



The discrepancy between the temperatures derived from 

 the observations with my first pyrometer and the present are 

 considerable, but may be sufficiently accounted for by the dif- 

 ferences in the circumstances of the experiments, without im- 

 puting inaccuracy to the instrument. In the paper to which 

 I have before alluded, I stated that " I did not offer the re- 

 sults as positive and accurate determinations of the diffl-rent 

 degrees, but only as nearer approximations than any that had 

 yet been furnished from actual observation. The only method 

 which I had it in my power to adopt for the purpose, I do 

 not consider to be susceptible of absolute accuracy. 'J^lie ar- 

 rangement made consisted of a muffle of black-lead placed in 

 an excellent draught-furnace. This muffle was furnished with 

 a door, through a round hole in which the stem of tiie pyro- 

 meter was passed up to the shoulder. Another door, which 

 •could be stopped at pleasure, admitted a full view of the in- 

 terior. 



