ANNALS 



OF 



PHILOSOPHY, 



AUGUST, 1824. 



Article I. 



Remarks on Solar Light and Heat. By Baden Powell, MA. of 

 Oriel College, Oxford, and FRS. 



{Continued from vol. vii. p. 406.) 



(27.) In the conclusion of a former paper I alluded to some 

 further experiments which were to follow, relative to the ques- 

 tion of the proportion obtaining between the heating and illumi- 

 nating effects of the solar rays. The method of experimenting 

 alluded to is one which I have not been able to apply to any 

 extensive series of different intensities. It consists in compar- 

 ing the effect produced on a blackened thermometer by the 

 focal light of different lenses, with the relative calculated inten- 

 sities of the rays in those foci. Thus we may ascertain whether 

 at these high intensities the same proportion is maintained. 

 Without proof we cannot assume that it is ; and a very few 

 comparisons may be sufficient to show, whether the proportion 

 is nearly preserved, or whether there be any considerable devia- 

 tion from it. 



(28.) When thermometers are exposed to the action of radiant 

 matter there are several considerations to be attended to in 

 comparing their observed risings ; and it will be convenient in 

 the first instance to bring these considerations into one point of 

 view. 



A thermometer exposed to radiant matter absorbs heat only 

 on one-half of its surface, while the other half is radiating again 

 its acquired heat, and the observed effect depends upon the 

 equilibrium which obtains between them. In particular cases 

 only part of one surface may be exposed to heat: the difference 

 between such part and the whole surface, together with the 

 absorbing and radiating powers of the surface, must, therefore, 

 be taken into consideration, as also the rate of communication 

 of heat dependent on the mass. 

 Neiv Series, vol. vm. o 



