5o6> Dr. Herschei/s Experiments on the solar, and 



A mean between the two gives ,4,29. Gold paper, therefore, 

 scatters only 429 rays of heat, and no less than 124371 rays 

 of light. 



219^ Experiment. 



Black velvet. Gold paper scattering. 



5 53i 5^... i|:f = ,556 



I turned the tablets, in order to ascertain the difference. 



Gold paper. Black, velvet. 



5 5*i 53- -i : 1t = ,6oo 



From a mean of both it appears, that when black velvet 

 scatters 1000 rays of heat, and only 7 rays of light, gold paper, 

 on the contrary, scatters no more than 578 rays of heat, but 

 124371 of light. 



Art. vii. — Whether Light and Heat be occasioned by the same, 



or by different Rays. 



Before we enter into a discussion of this question, it appears 

 to me that we are authorised, by the experiments which have 

 been delivered in this Paper, to make certain conclusions, that 

 will entirely alter the form of our inquiry. Thus, from the 18th 

 experiment it appears, that 21 degrees of solar heat were given 

 in one minute to a thermometer, by rays which had no power 

 of illuminating objects, and which could not be rendered visible, 

 notwithstanding they were brought together in the focus of a 

 burning lens. The same has also been proved of terrestrial 

 heat, in the 9th experiment ; where, in one minute, 39 degrees 

 of it were given to a thermometer, by rays totally invisible, even 

 when condensed by a concave mirror. Hence it is established, 



