Daniell on a "New Pyrometer. 317 



I do not offer them as positive and accurate determinations of 

 the different degrees, but only as nearer approximations than 

 any that have yet been furnished from actual observation. The 

 only method which I have yet had it in my power to adopt for 

 this purpose, I do not consider to be susceptible of absolute ac- 

 curacy. The arrangement 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 the pyrometer was passed up to the shoulder. Another hole 

 in the top of the door which could be stopped at pleasure, ad- 

 mitted a full view of the interior. The metal to be tried was 

 placed in a small black-lead receptacle of the same thickness 

 as ths pyrometer tube, in the middle of the muffle. Now it is 

 evident that the pyrometer so situated would indicate the mean 

 heat of the whole of the muffle, which heat might and did vary 

 in different parts. Of two pieces of silver, of the same size, 

 placed within an inch of each other, one fused some time before 

 the other. Every precaution was taken to place the metal to 

 be tried as near as possible to that part where the mean heat 

 probably existed, but still the method is not susceptible of ex- 

 treme precision. Means might be contrived to surround the in- 

 strument with the metal in a state of fusion much in the same 

 manner as it is surrounded with mercury for the purpose of 

 graduation, but this would require particular opportunities 

 which it is to be hoped that those will avail themselves of who 

 have them in their power. The experiments were repeated 

 more than once with a very close agreement of results, but the 

 fusing point of silver is most to be relied on, as having been 

 furnished by three different trials, all of them agreeing to a 

 degree. 



