and the Mode of its Communication. 61 



previous trials, that the instrument was not sensibly 

 affected by a bright metallic surface being presented to 

 it, provided the temperature of the metal and that of 

 the instrument were the same, I now withdrew one of 

 the cylindrical vessels, and, taking it into another room, 

 I filled it with pounded ice and water. 



Entering the room again, I now presented the flat 

 vertical bottom of this horizontal cylindrical vessel, 

 filled with ice and water, to one of the balls of the ther- 

 moscope at the distance of four inches. 



The bubble of spirit of wine began instantly to 

 move with a slow, regular motion towards the cold 

 body ; and, having advanced in the tube about an inch, 

 it remained stationary. 



On bringing the cold body nearer the ball to which it 

 was presented, the bubble was again put in motion, and 

 advanced still farther towards the cold body. 



Experiment No. 18. Although the result of the fore- 

 going experiment appeared to me to afford the most 

 indisputable proof of the radiation of cold bodies, and 

 that the rays which proceed from them have a power of 

 generating cold in warmer bodies which are exposed to 

 their influence, yet in a matter so extremely curious, 

 and of such high importance to the science of heat, I 

 was not willing to rest my inquiries on the result of a 

 single experiment. 



In order to vary the substance, or species of matter, 

 presented cold to the instrument, and at the same time 

 to remove all suspicion respecting the possibility of the 

 effects observed being produced by currents of cold air 

 occasioned in the room by the presence of the cold 

 body, I now repeated the experiment with the following 

 variations. 



