Radiation of Heat by Gaseous Matter. 341 



Tabulating the results so as to place each deflection beside the 

 vapour-tension which produces it, we have the following view of 

 the experiment : — 



Table V. — Dynamic Radiation of Boracic Ether. 



Tension in parts 

 of an atmosphere. Deflection. 



1 



o 



-th 56 



300 



1 x-^= *:j h 42 



150 300 45000 



_i_x-i-x-!-= I th 20 



150150 300 67 50000 



1_ y 1 y 1 X 1 — 1 f Q 14 



150 150 150 300 101^500000 



The air itself, slightly warming the apparatus near the pile, 

 produces a feeble radiation, amounting to 6° or 7°. I have pur- 

 posely excluded the deflection 10°, in order to show that the 

 effect was still diminishing when the experiment ended, the con- 

 stant effect due to the air itself being not yet attained. I thus 

 exclude two Os from the denominator of my fraction which might 

 fairly have appeared in it. The above result is, however, suffi- 

 ciently extraordinary, showing as it does that the radiation of an 

 amount of vapour possessing in our tube a tension of less than 

 the thousand millionth of an atmosphere is perfectly measurable. 

 It will also be borne in mind that the temperature imparted to 

 this infinitesimal quantity of matter did not exceed 0*75 of a 

 Centigrade degree. 



These experiments, which I intend to develope on a future 

 occasion, seem to give us new ideas as to the nature and capabi- 

 lities of matter. A platinum wire raised to whiteness in a vacuum 

 by an electric current, becomes comparatively cold in a second 

 after the current has been interrupted; yet that wire, while 

 ignited, was the repository of an immense amount of mechanical 

 force. What has become of this ? It has been conveyed away 

 by a substance so attenuated that its very existence must for ever 

 remain a hypothesis. But here is matter that we can weigh, 

 measure, taste, and smell — that we can reduce to a tenuity which, 

 though expressible by numbers, defeats the imagination to con- 

 ceive of it. Still we see it competent to arrest and originate 

 quantities of force which in comparison with its own mass are 

 almost infinite, a small fraction of this force causing the double 

 needle of the galvanometer to swing through considerable arcs. 

 When we find common ponderable matter producing these effects, 

 we have less difficulty in investing the luminiferous ether with 

 those mechanical properties which have long excited the interest 

 and wonder of all who have reflected upon the circumstances in- 

 volved in the undulatory theory of light. 



