196 Historical Review of Experiments 



The mercury in the thermometer rose in the follow- 

 ing manner : After the instrument had remained in the 

 boiling water i min. 30 sec. the mercury had risen from 

 1 8 to 27. After the lapse of 4 minutes, it had risen 

 to 44 T 9 o:> and at the end of 5 minutes to 48 J. 



In order to estimate more accurately the relative 

 rapidity with which heat passed through a vacuum and 

 through air, I broke off the end of the small pointed 

 tube which projected from the under side of the globe 

 so that the air could freely enter the globe ; I then 

 melted the tube together a second time, by means of a 

 candle ; cooled my apparatus in water, and plunged it, 

 as soon as it had acquired the temperature of this water, 

 that is 1 8, again into boiling water. The mercury rose 

 much more rapidly than in the preceding experiment. 



The manner in which the temperature gradually in- 

 creased in both experiments is shown in the following 

 table. 



When the spherical reservoir of the mercurial ther- 

 mometer, which was fastened in the centre of a glass 

 globe an inch and a half in diameter, was plunged into 

 boiling water, the times of ascent were as follows : 



In a Torricellian vacuum. Surrounded by air. 



(Exp. No. i.) (Exp. No. 2.) 



Time Heat Time Heat 



elapsed. acquired. elapsed. acquired. 



Upon being plunged into ~> fi0 Q0 



boiling water } 



m. s. o m. s. o 



After remaining in it I 30 27 o 45 27 



4 o 44-fr 2 10 44^ 



5 6 4 8J- 50 6o T % 



From the results of these experiments it is evident 

 that the heat increases nearly twice as fast when the bulb 

 is surrounded by air as when it is in a vacuum. 



I afterwards performed other experiments of the same 



