2g2 Sir Benjamin Thompson’s 
thermometer N° 3. was conftrutfled with a view to thofe expe- 
riments \ and having now provided myfelf with a flock of thofe 
different kinds of airs, I began with fixed air , with which, by 
aftiftance of this inftrumemt, to determine pofitively with regard to the pafTage of 
heat in the Torricellian vacuum: and this, I think, I have done, notwithftanding 
that an unfortunate accident put it out of my power to purfue the experiments fo 
far as I intended. 
This inftrument being fitted to a fmall ftana or foot of wood, in fuch a manner 
that the glafs body remained in a perpendicular fituation,. I placed it in my room, 
by the fide of another inclofed thermometer (N° 2.)r which was furrounded by 
air, and obferved the effedl of the variation of heat irr the atmofphere.- I foon 
difcovered, by the motion of the mercury in the inclofed thermometer, that the 
heat paffed through the Torricellian vacuum ; but it appeared plainly from the 
fiuggifhnefs or great infenfibility of the thermometer, that the heat paffed with 
much greater difficulty in this medium than in. common air* I now plunged both 
the thermometers into a bucket of cold water ; and I obferved that the mercury 
in the thermometer furrounded by air defcended much fafter than that in the 
thermometer furrounded by the Torricellian vacuum. I took them out of the 
cold water, and plunged them into a veffel of hot water (having no conveniencies 
at hand to repeat the experiment in form with the freezing and with the boiling 
water); and the thermometer furrounded by the Torricellian vacuum appeared: 
flill to be much more infenfible or fluggilh than that furrounded by air. 
Thefe trials were quite fufficient to convince me of the pafTage of heat in the 
Torricellian vacuum, and alfo of the greater difficulty of its pafTage in that 
medium than in common air ; but, not fatisfied to reft my inquiries here, I took 
the firft opportunity that offered, and fet myfelf to repeat the experiments which 
1 had before made with the inftruments N° I. and N° 2. I plunged this inftru- 
ment into freezing water, where I let it remain till the mercury in the inclofed 
thermometer had defcended to o° ; when, taking it out of the freezing water, I 
plunged it fuddenly into a vefiel of boiling wafer, and prepared myfelf to obferve 
the afcent of the mercury in the inclofed thermometer as in the foregoing experi- 
ments ; but unfortunately the moment the end of the g-lafs body touched the 
boiling water, it cracked with the heat at the point where it had been hermetically 
fealed, and the water rufhing into the body, fpoiled the experiment : and I have 
-not fince had an opportunity of providing myfelf with another inftrument to 
-repeat it. 
meaft$ 
