MEMOIR XXVIII.] DISTRIBUTION OF HEAT IN THE SPECTRUM. 493 



heat observed did not pre-exist in the incident rays : it is 

 the result of their extinction. 



The remark has been made that these results are es- 

 sentially connected with photometry. In fact, any ther- 

 mometer is converted into a photometer if its ball or 

 other receiving surface be coated with a perfectly opaque 

 non-reflecting substance. 



