in various Substances. 423 



ing any Heat at all, or at least any sensible quantity. I 

 therefore flattered myself with hopes of being able, with 

 the assistance of this instrument, to determine positively 

 with regard to the passage of Heat in the Torricellian 

 vacuum : and this I think I have done, notwithstand- 

 ing an unfortunate accident that put it out of my power 

 to pursue the experiment so far as I intended. 



This instrument being fitted to a small stand or foot 

 of wood, iri such a manner that the glass body remained 

 in a perpendicular situation, I placed it in my room, by 

 the side of another inclosed thermometer (No. 2) which 

 was surrounded by air, and observed the effects produced 

 on it by the variation of Heat in the atmosphere. I 

 soon discovered, by the motion of the mercury in the 

 inclosed thermometer, that the Heat passed through the 

 Torricellian vacuum ; but it appeared plainly, from the 

 sluggishness or great insensibility of the thermometer, 

 that the Heat passed 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 ob- 

 served that the mercury in the thermometer surrounded 

 by air descended much faster than that in the thermome- 

 ter surrounded by the Torricellian vacuum. I took 

 them out of the cold water, and plunged them into a 

 vessel of hot water (having no conveniences at hand to 

 repeat the experiment in due form with the freezing 

 and with the boiling water); and the thermometer sur- 

 rounded by the Torricellian vacuum appeared still to be 

 much more insensible or sluggish than that surrounded 

 by air. 



These trials were quite sufficient to convince me of 

 the passage of Heat in the Torricellian vacuum, and also 

 of the greater difficulty of its passage in that medium 



