C 187 7 
IX. An experimental enquiry into the nature of the radiant heat- 
ing effects from terrestrial sources. By Baden Powell, M. A. 
F. R. S. of Oriel College, Oxford. 
Read February 17, 1825. 
(1.) The nature of the heating effect emanating from lumi- 
nous hot bodies has been distinctly shown to be, in many 
particulars, very different from that evolved from non-lumi- 
nous sources ; but the ideas commonly entertained on the 
subject, are far from being precise and distinct. To gain if 
possible some ground for establishing more clear views, is 
the object of the following enquiries. 
(2.) Professor Leslie, in his well known and elegant expe- 
riments, (Inquiry concerning Heat, &c. chap, iii.) has fully 
established the theory of the effect of screens on radiant heat ; 
and these effects give some of the most important criteria for 
examining the nature of radiating agents. 
Those experiments apply only to the heat evolved from, a 
non-luminous source. It therefore naturally becomes the 
subject in question, whether the interceptive power of glass 
is not limited to a certain temperature, or state, of the radi- 
ating source ; and to this point accordingly the attention of 
several eminent observers has been directed in many well 
known investigations, among which those of M. De La 
Roche are justly regarded as the most important and com^ 
plete. In these experiments it appears, that a greater effect 
