on the Subject of Heat. 223 



a series of experiments on the subject of radiant heat, 

 and in my sixth Essay, which treats Of the Manage- 

 ment of Fire and the Economy of Fuel, published at 

 London in 1797, I had openly announced my purpose 

 of taking the work in hand as soon as possible. 



The experiments I have just mentioned as being 

 performed in my presence by Professor Hope deter- 

 mined me not to put off this intention of mine a 

 moment longer. 



As soon as I returned to London, I began imme- 

 diately to make all preparations for my researches. I 

 therefore communicated my intentions to Sir Joseph 

 Banks, at that time President of the Royal Society, 

 also to Mr. Cavendish, because both these gentlemen 

 (as well as myself) were managers of the Royal In- 

 stitution. As I wished to carry out my experiments 

 in the most decisive manner, and consequently with 

 the apparatus as perfect as possible, which to all 

 appearance would require a considerable outlay, I 

 was, at my request, authorized by the managers of 

 the Royal Institution to procure the new instruments 

 needed at the expense of the Institution, with the con- 

 dition, however, that these instruments should remain 

 at the Institution as its property, and be kept in its 

 cabinet. 



As the principal object in this investigation was to 

 establish beyond doubt the cooling emanations from 

 cold bodies, I desired to accumulate the emanations and 

 concentrate them as much as possible, in order, that 

 their action might be so much the more sensible. 



D 



Pictet took for his experiment, as is well known, two 

 metallic reflectors, and placed a cold body in the focus 

 of one of them, and a thermometer in the focus of 



