C 372 2 
XXVI. An account of some experiments relative to the passage 
of radiant heat through glass screens. By the Rev. Baden 
Powell, M. A. F. R. S. of Oriel College , Oxford. Commu- 
nicated March 9, 182,6. 
Read June 1, 1826. 
(1) In a former Paper, communicated to the Royal Society, 
and which has been honoured with a place in the Philoso- 
phical Transactions for 1825, I attempted an investigation of 
the distinctive characters of two species of heating effect, in 
which particular reference was made to the action of trans- 
parent screens. In the present communication, my object is 
to examine a further point belonging to that part of the sub- 
ject ; and to which, as well as the former enquiry, I have 
been led, from considering the results obtained by M. De La 
Roche. The investigation given in my former paper pro- 
ceeded upon the assumption, that simple radiant heat is in- 
capable of permeating glass by direct transmission when the 
source is below luminosity : and the conclusion deduced 
from my experiments went to show, that that portion of the 
heat which is intercepted above luminosity, is simple heat, 
unaltered except in intensity, whilst that which is transmitted 
is of a different kind. 
That this assumption, at least under all ordinary cir- 
cumstances, is warranted by most decisive experiments, I 
conceive sufficiently certain. It appears to me, however, that 
