VOL. LXXIV.] PHILOSOPHICAL TRANSACTIONS. 577 



similarity in the aspect of the different parts; whereas in small fires, the difference 

 not only between the two ends of the muffle, but in much less distances, is such 

 as to strike the eye at once. When the muffle appeared of a low red heat, such 

 as was judged to come fully within the province of my thermometer, it was 

 drawn forward, towards the door of the oven; and its own door being then 

 nimbly opened by an assistant, I immediately pushed the silver piece as far as it 

 would go. But as the division which it went to could not be distinguished in 

 that ignited state, the muffle was lifted out, by means of an iron rod passed 

 through two rings made for that purpose, with care to keep it steady, and avoid 

 any shake that might endanger the displacing of the silver piece. 



When sufficiently cooled to be examined, I noted the degree of expansion 

 which the silver piece stood at, and the degree of heat shown by the thermo- 

 meter pieces measured in their own gage ; then returned the whole into the oven 

 as before, and repeated the operation with a stronger heat, to obtain another 

 point of correspondence on the two scales. The first was at 2±-° of my thermo- 

 meter, which coincided with 66° of the intermediate one; and as each of these 

 last has been before found to contain 20 of Fahrenheit's, the 66 will contain 

 1320; to which add 50, the degree of his scale to which the O of the interme- 

 diate thermometer was adjusted, and the sum, 1370, will be the degree of 

 Fahrenheit's corresponding to my 2\°. 



The 2d point of coincidence was at 6\° of mine, and 92° of the intermediate; 

 which Q2 being, according to the above proportion, equivalent to 1840 of Fah- 

 renheit, add 50 as before to this number, and my 6\° is found to fall on the 

 1 890th degree of Fahrenheit. It hence appears, that an interval of 4° on mine 

 is equivalent to an interval of 520° on his; consequently 1 of mine to 130° of 

 his; and that the O of mine corresponds to his 1077-5°. Several other trials were 

 made, which gave results so nearly alike, that I have little apprehension of any 

 material error. 



From these data it is easy to reduce either scale to the other through their 

 whole range; and from such reduction it will appear, that an interval of near 

 480° remains between them, which the intermediate thermometer serves as a 

 measure for; that mine includes an extent of about 32000 of Fahrenheit's de- 

 grees, or about 54 times as much as that between the freezing and boiling points 

 of mercury, by which mercurial ones are naturally limited; that if the scale of 

 mine be produced downwards, in the same manner as we have supposed Fahren- 

 heit's to be produced upwards, for an ideal standard, the freezing point of water 

 would fall nearly on 8° below O of mine, and the freezing point of mercury a 

 little below 8-i- ; and that therefore, of the extent of now measureable heat, 

 there are about T V of a degree of my scale from the freezing of mercury to the 



vol. xv. 4 E 



