and Polarization of Heat. 135 
deviation (at which, after several oscillations, it is finally to settle) 
could afford. Not only does the acquired velocity frequently carry 
it through double the space due to the statical effect ; but I have 
observed that the action of the thermo-electric pile so far resembles 
that of the voltaic, that we appear to have an excess of effect at the 
first moment of action, which gives a greater deviation than can be 
afterwards obtained *. It is therefore to be recollected, that in 
speaking confidently of effects, which, statically speaking, are ex- 
ceedingly small, the experimentalist has a species of evidence far 
stronger than the mere numerical expression of the deviation of 
the needle, but the degree of which must be taken on the faith 
of his veracity. Thus I have obtained repeated differences, not 
exceeding half or even a quarter of a degree of the multiplier 
(observed without a telescope), which, by the promptitude with 
which the needle was repelled or attracted at the instant that the 
change of circumstances to be considered was effected, left as little 
doubt in my mind as if the numerical result had been many times 
greater. 
9. Having satisfied myself, in a variety of ways, of the ex- 
treme delicacy and promptitude of action of this instrument, I 
thought of applying it to detect the heat of the moon’s rays in a 
more unexceptionable manner than, I am persuaded, it has ever 
been attempted. This curious question had not escaped MM. 
Nosrz1 and Metionr when they first constructed the instru- 
ment, and they mention in their first account of the thermo-mul- 
* This remarkable effect, which may be described as an increase of tension by 
confinement, seems generally to exist where the conductors of imponderable agents 
oppose considerable resistance to their passage. It is familiar in Voltaic electricity, 
and I have often observed it in magnetic electricity. It is similar to the action 
which I have attempted to demonstrate in the passage of heat from good to bad con- 
ductors (see the 12th Volume of these Transactions), where we have the full advan- 
tage of the dynamical effect ; whilst the existence of statical tension in heat seems 
likewise to be proved (as we might have anticipated) by the beautiful experiment 
described by Professor Powett in the Philosophical Transactions for 1834. 
