318 Daniell on a Neto Pyrometer. 



These four last points were all determined by placing the 

 muffle over two Argand lamps. 



Pyrom. Therm. 



Fusing point of brass .... 267 = 1869 



Ditto pure silver ..... 319 = 2233 



Ditto copper 364 = 2548 



Ditto gold 370 = 2590 



Ditto cast iron 49/ = 3479 



A red heat just visible in the day- 

 light is about 140 = 980 



The heat of a common parlour fire 163 = 1141 



The difference between most of these results, and those of 

 Mr. Wedgwood is indeed enormous. His determination of 

 the same points is as follows :— 



Pyroin. Tlierm. 



Mercury boils —2.-^^^^= 600 



Red heat fully visible in the 



dark ....'... -1. =947 



Ditto in the day-light . . 0. =1077 



Brass melts -|-21 = 3807 



Copper 27 = 4587 



Fine silver 28 =4717 



Fine gold 32 = 5237 



Cast iron 130 =17977 



When the nature of the two pyrometers is considered, and the 

 principles upon which they are founded, there will not exist, I 

 trust, much doubt, as to the degree of confidence to which each 

 is entitled. It must be recollected, that the equal expansion of 

 platinum, with equal increments of heat, is one of the best 

 established facts of natural philosophy, while the equal con- 

 traction of clay, is an assumption which has been disputed, if 

 not disproved. The instrument which I have proposed, has 

 the further advantage of confirming the indications of its as- 

 cent when heating, by its gradual return to its original state 

 when cooling, an advantage which is totally uncompensated 

 in that of Mr. Wedgwood. There- is yet, another argument, 



