on the Subject of Heat. 229 



further except that it made a firm and lasting impression 

 on my mind, and afterwards exerted much influence on 

 the manner in which I carried on my inquiries. 



Meanwhile I did not allow this occurrence to hinder 

 me in the least from carrying out to the end the experi- 

 ments for which I had devised my apparatus. I had, 

 therefore, a cylindrical iron stove put into the middle 

 of a large room, and having surrounded it with fire- 



o y o 



screens, I caused all the windows in the room to be 

 opened. When the stove was sufficiently heated, I 

 found that no sensible change had taken place in the 

 mean temperature of the room. I now removed the 

 screens which surrounded the stove, and placed all three 

 of the boxes at the same time in the same position, that 

 is, twenty-four inches from the stove. 



The box containing the iron disk, which previously 

 had contained the most heat after standing in the rays 

 of the sun, was also now the warmest after being sub- 

 jected to the influence of the rays which proceeded, 

 although invisibly, from the stove. 



In order to become more closely acquainted with 

 these rays, I had several new instruments constructed ; 

 among others, four large air thermometers, and three 

 other thermometers of the sa*ne size filled with spirit 

 of wine. The bulbs of these thermometers were an 

 inch and three quarters in diameter, and contained either 

 various substances mixed with air or else simply spirit 

 of wine. The bulb of the first thermometer was filled 

 with air alone; in the second was a mixture of air and 

 eider-down ; in the third a mixture of air and very 

 thin flat silver threads ; the fourth contained air, eider- 

 down, and, at the same time, flat silver threads. 



In the bulb of the first of the thermometers filled 



