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' i\". 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' 10". 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 2"^ (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 

 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. 



