Experiments upon Heat . 281 
Of thefe inftruments I provided myfelf with two, as nearly 
as poffible of the fame dimenfions ; the one, which I fhall 
call N 9 i. being voided of air, in the manner above defcribed ; 
the other, N° 2. being filled with air, and hermetically fealed. 
With thefe two inftruments (fee fig. 2.) I made the follow- 
ing experiments upon the nthof July 1 aft, at Manheim, be- 
tween the hours of ten and twelve, the weather being very 
fine and clear, the mercury in the barometer {landing at 27 
inches 11 lines, Reaumur’s thermometer at 15 0 , and the quill 
hygrometer of the Academy of Manheim at 47°. 
Experiments N° 3, 4, 5 and 6. 
- 
Putting both the inftruments into melting ice, I let them 
remain there till the mercury in the inclofed thermometers 
refted at the point o°, that is to fay, till they had acquired 
exadlly the temperature of freezing water or melting ice ; and 
then taking them out of the ice I plunged them fuddenly into 
a large veffel of boiling- water, and obferved the time required 
‘for the mercury to rife in the thermometers from ten degrees 
to ten degrees, from o° to So°, taking care to keep the water 
conftantly boiling during the whole of this time, and taking 
care alfo to keep the inftruments immerfed to the fame depth, 
that is to fay, juft fo deep that the point o° of the inclofed 
thermometer was even with the furface of the water. 
Thefe experiments I repeated twice, with the utmoft care ; 
and the following table gives the refult of them, 
. ...... ■ (-■ • 
Vol. LXXVI. 
P P 
Ther- 
