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. 

 Nobili and Melloni 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 Powell in the Philosophical Transactions for 1834. 



