REPORT ON THERMO-ELECTRICITY. 
301 
In elastic media radiation can commence and continue; but 
they are still worse conductors. 
In vacuo it might be presumed by analogy that a yet more 
free radiation might take place ; yet some experiments (as we 
have seen,) show the contrary; and here there is no conduction. 
With regard to that portion of the heat which accompanies 
or belongs to light, the theory which I originally suggested, 
(merely as an hypothesis representing the facts,) viz. that it was 
simply the latent heat of light, developed of course when the light 
was absorbed, is connected with the hypothesis of the materiality 
of light; but it may be worth inquiry whether it does not apply 
even better to the elastic aether , in wdiose undulations light is 
now proved to consist. 
Report on Thermo-electricity. By the Rev. James Cumming, 
F.R.S., Professor of Chemistry in the University of Cam¬ 
bridge. 
In communicating to the members of this Society an outline of 
the progress and present state of Thermo-electricity, I con¬ 
gratulate both them and myself on the allied branches of science 
having fallen into such able hands, that I should not be justified, 
even if it were my wish, to extend this Report beyond its im¬ 
mediate subject. 
On one point more particularly I am happy,—since w T e are not 
so fortunate as to receive instruction from the discoverer him¬ 
self,—that Dr. Ritchie has undertaken to exhibit and explain 
to us the recent researches of Mr. Faraday. The continuous 
electrical currents, now made known to us by these experiments, 
seem so much more nearly connected with those in the thermo¬ 
electric circuit, than with those peculiar either to the common 
or galvanic electricity, that I should otherwise have thought it 
incumbent on me to make the notice of them a part of this Re¬ 
port. Divested, as the subject will thus be, of all extraneous 
matter, I shall therefore be enabled to say all that I think to 
be really necessary, and yet detain you but a short time from 
more important communications. 
On a review of the labours of different experimentalists on 
Thermo-electricity, it soon became evident to me, that, to give 
anything like aluminous account of them, it would be necessary 
to make some attempt at a classification of their objects. This, 
I must confess, was no very easy matter; for in this, as in some 
other branches of experimental inquiry, I have found it difficult, 
