ANNALS 



OF 



PHILOSOPHY. 



JUNE, 1824. 



Article I. 



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

 Oriel College, Oxford. 



(Continued from p. 328.) 



(18.) In attempting an inquiry into the constitution of the 

 solar rays in reference to their heating power, I made the simple 

 experiment described in my former communication, under an 

 impression that every step in such an inquiry ought to be taken 

 with the utmost caution ; and that no position however probable 

 ought to be assumed till sufficiently examined by experiment. 

 Those experiments appear to me to prove that in the solar rays 

 no free uncombined radiant heat exists, at least in any quantity 

 sufficient to produce a rise of a quarter of a centigrade degree, 

 on a thermometer coated with a wash of chalk. The same 

 point, however, may be put to a more accurate and delicate test 

 by means of Leslie's differential thermometer — an effect corre- 

 sponding to the twentieth part of a centigrade degree may be 

 thus rendered sensible. — (See Leslie on Heat, p. 1 1 and 420, and 

 Treatise on Instruments, p. 10.) 



Being particularly desirous of ascertaining whether it were 

 possible to detect the smallest appreciable degree of simple 

 radiant heat in the natural state of the solar rays, I continued 

 the examination of the point by the following application of the 

 differential thermometer. The instrument employed was of the 

 " stationary" kind, the sentient ball was blown of black glass, 

 and the halves of degrees could be very readily observed on its 

 scale. 



New Series, vol. vn. 2 n 



