XXVI. An account of some experiments relative to the passage of radiant heat through glass screens

Abstract

(1) In a former Paper, communicated to the Royal Society, and which has been honoured with a place in the Philosophical 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 transparent screens. In the present communication, my object is to examine a further point belonging to that part of the subject; 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 proceeded upon the assumption, that simple radiant heat is incapable 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 circumstances, is warranted by most decisive experiments, I conceive sufficiently certain. It appears to me, however, that in reference to its strict universality, some further enquiry is necessary. The general inference respecting transmission, deduced from De La Roche's experiments, has, I conceive, been satisfactorily explained by mine; but there is one of his conclusions to which my principle does not apply (except in a particular case), and which might seem to afford considerable ground for the idea of an actual radiation through glass, under particular circumstances.