224 Historical Review of Experiments 



the other. That the cooling influence which the cold 

 object exerted on the thermometer might be doubled, 

 I proposed in my experiment to have two cold bodies 

 and one reflector, and, in order to increase so much the 

 more the cooling effect on the thermometer, I intended 

 to place it in the upper part of an open cylindrical 

 vessel, the two cold bodies, however, being placed some- 

 what lower. 



In Pictet's experiments both reflectors were in a hori- 

 zontal line, and the thermometer on which the cooling 

 influences were exerted was continually heated by the 

 vertical current from the air above, which was caused 

 necessarily by the cooling of the stratum of air immedi- 

 ately surrounding the thermometer; as a consequence, 

 the frigorific influence of the cold body was lessened by 

 the calorific influence of this current to such an ex- 

 tent that an equilibrium resulted. Still I expected that 

 in my case I should, in all probability, be able to carry 

 the cooling of the thermometer still farther, as I hoped 

 by the arrangement of my apparatus to prevent this 

 current, and at the same time to double the cooling 

 effect. 



After long delay on the part of the workmen, the 

 necessary mirrors, four in number, were finally com- 

 pleted. They are now in the physical cabinet of the 

 Royal Institution at London, and are used in the an- 

 nual lectures on physics. If I am not mistaken, there 

 are several other instruments kept in the same place, 

 which I had expected to use in the projected experi- 

 ments on the radiation of bodies ; but most of the in- 

 struments designed for this investigation (made by Mr. 

 Fraser, New Bond Street) were made at my own ex- 

 pense and are still in my possession. 



