VOL. LXXVI.") 



PHILOSOPHICAL TRANSACTIONS. 



113 



Thermometer N° 1 . 

 Time elapsed • tt * i ^ 



Exp.N°7. Exp.N°8. Heat lost. 



2* 

 58 

 17 

 46 



5 

 74 

 42 



54' 



2 

 18 

 2,7 

 16 

 10 

 59 



80° 

 70 

 60 

 50 

 40 

 30 

 20 

 10 

 



Not observed. Not observed. 

 Total time of cooling from 80° to 10° 

 In Exp N° 7.= ifi" 4' 

 In Exp. N°8. = \6 l6 

 Medium = l6 10 



Thermometer N° 2. 

 Time elapsed. tr .. i 4. 



Exp.N°9. Exp.N°10. "eat lost. 



33* 0" 3J' 



39 34 



44 44 



55 55 



17 1 18 



57 1 57 



44 3 40 



10 Not observed. 

 Total time of cooling from 80° to 10**. 

 In Exp. N° 9- = 9"" 49' 

 In Exp. N° 10. =9 41 

 Medium = 9 45 



0" 

 

 

 

 1 

 1 

 3 

 40 



80° 

 70 

 60 

 50 

 40 

 30 

 20 

 10 

 



By these experiments it appears, that the conducting power of air is to that of 

 the Torricellian vacuum as Qff to l6-^ inversely, or as 1000 to 603. 



To determine whether the same law would hold good when the heated ther- 

 mometers, instead of being plunged into freezing water, were suffered to cool in 

 the open air, I made the following experiments. The thermometers N° 1 

 and ]SI° 2 being again heated in boiling water, as in the last experiments, I took 

 them out of the water, and suspended them in the middle of a large room, 

 where the air (which appeared to be perfectly at rest, the windows and doors 

 being all shut) was warm to the l6th degree of Reaumur's thermometer, and 

 the times of cooling were observed as follows. 



Exp. N° 11. 



Thei-mometer N° 1. 



Surrounded by a Torricellian vacuum. 



Heated to 80°, and suspended in the open 



air warm to l6°. 



Time elapsed. 



Not observed. 

 I" 24' 



1 44 



2 28 

 4 16 



Heat lost. 

 80° 

 70 

 60 

 50 

 40 

 30 



10 12 = total time employed in 

 cooling from 70° to 30°. 



Exp. N° 12. 



Thermometer N° 2. 



Surrounded by air. 



Heated to 80°, and suspended in the open 



air warm to l6°. 



Time elapsed. 



Not observed. 

 O- 51' 



1 5 

 . 1 34 



2 41 



Heat lost. 

 80° 

 70 

 60 

 50 

 40 

 30 



6 11 = total time employed in 

 cooling from 70° to 30°. 



Here the difference in the conducting powers of air and of the Torricellian 

 vacuum appears to be nearly the same as in the foregoing experiments, being as 

 6-^ to 10|4 inversely, or as 1000 to 605. 



As it might possibly be objected to the conclusions drawn from these experi- 

 ments that, notwithstanding all the care that was taken in the constructing of 



VOL. XVI. Q 



