in various Substances. 421 



Time from 70 to 30= 8' o" ; but in the experiment 

 No. 12, with the thermometer No. 2, the time employed 

 in cooling from 70 to 30 was only 6' n". In this ex- 

 periment, with the thermometer No. 3, the time em- 

 ployed in cooling from 60 to 30 was 7' 48"; but in 

 the above-mentioned experiment, with the thermometer 

 No. 2 it was only 5' 20". It is true, the air of the 

 room was somewhat cooler when the former experiment 

 was made, than when this latter was made, with the ther- 

 mometer No. 3 ; but this difference of temperature, 

 which was only i\ (in the former case the thermometer 

 in the room standing at 16, and in the latter at 18^), 

 certainly could not have occasioned the whole of the ap- 

 parent difference, in the results of the experiments. 



Does air receive Heat more readily than it parts with 

 it? This is a question highly deserving of further in- 

 vestigation, and I hope to be able to give it a full ex- 

 amination in the course of my projected inquiries; but 

 leaving it for the present, I shall proceed to give an ac- 

 count of the experiments which I have already made. 

 Conceiving it to be a step of considerable importance 

 towards coming at a further knowledge of the nature of 



o o 



Heat, to ascertain, by indisputable evidence, its passage 

 through the Torricellian vacuum, and to determine, with 

 as much precision as possible, the law of its motions in 

 that medium ; and being apprehensive that doubts 

 might arise with respect to the experiments before de- 

 scribed, on account of the contact of the tubes of the 

 inclosed thermometers in the instruments made use of 

 with the containing glass globes, or rather with their 

 cylinders: by means of which (it might be suspected) 

 that a certain quantity, if not all the Heat acquired, 

 might possibly be communicated ; to put this matter 

 beyond all doubt, I made the following experiment. 



