228 Transmission of Radiant Heat 



two and three hundred pounds, having been hfted on the fingers of 

 four persons with no more exertion on their part than would be re- 

 quired to hft a feather, I cannot avoid reverting to what Sir David 

 Brewster considers a possible explanation, illusion. One great source 

 of error, as I conceive, in the experiment, is that gentlemen do not 

 take the pains to compare at the time of trial the necessary exertion 

 when the prescribed process is used, with the necessary exertion 

 without preparation or under ordinary circumstances. 



Remark. — Some years ago, I was interested in the subject discuss- 

 ed above, and at the time when such experiments were mentioned 

 in the public prints, I was concerned in making them repeatedly on 

 others, and was the subject of them myself. I can only say, that 

 when the experiment was made according to the prescribed forms, 

 there was a very obvious apparent diminution of resistance in raising 

 or in being raised. — Ed. 



Art. V. — Transmission of Radiant Heat through different solid 

 and liquid bodies. — An abstract of a statement of the results ob- 

 tained by M. Melloni, from the Journal of the Institute. 



Translated from the Bib. Univ., by J. Griscom. 



Nothing can be more suitable than the instrument employed by 

 M. Melloni, for the purpose of rendering totally insensible the influ- 

 ence of the heat which emanates from the screen itself, without al- 

 tering the value of that which is immediately transmitted through it. 

 It is sufficient to say that, under convenient circumstances it renders 

 sensible the heat of a single person at the distance of 25 to 30 feet. 

 This instrument is composed of a thermo-electric pile, formed of 

 small bars of antimony and bismuth, disposed in a bundle, and of a 

 condensing or multiplying galvanometer whose extremities commu- 

 nicate, by means of two long copper wires, with those of the pile. 

 The rays from the heating source, fall on one of the ends of the 

 bundle which constitutes the pile, — this heat excites an electric cur- 

 rent which piervading the apparatus disturbs the equilibrium of the 

 magnetic needle of the galvanometer, the deviation of which shews 

 the intensity of the radiant heat. The instrument may be so adjust- 

 ed, that at a convenient distance from the heating source, the rays 

 falling directly on the pile, produce a deviation of 30°. When they 



