78 
PEOFESSOE TYNDALL ON THE ABSOEPTION AND 
Table V. — Dynamic Kadiation of Boracic Ether. 
Tension in parts 
of an atmosphere. 
Deflection. 
O 
56 
42 
20 
14 
The air itself, slightly warming the apparatus near the pile, produces a feeble radiation, 
amounting to 6° or 7°. I have purposely excluded the deflection 10°, in order to show 
that the effect was still diminishing when the experiment ended, the constant eflfect 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, 
sufficiently extraordinary, shoAving 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 capabilities of matter. A platinum wire raised to white- 
ness 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 1 It has been conveyed 
away by a substance so attenuated that its very existence must for ever remain an hypo- 
thesis. 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 
conceive of it. Still we see it competent to arrest and originate quantities of force, 
which on 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 involved 
in the undulatory theory of light. 
In the foregoing experiments dry air was used to warm the vapours, but similar difier- 
ences ought to be exhibited by gases when heated by their own dynamic action. This 
is the case, as the following experiments show : — 
Table VI. — Dynamic Radiation of Gases. 
Name. 
Eadiation. 
O 
Air . 
Oxygen 
Hydrogen 
Carbonic oxide 
Carbonic acid 
Nitrous oxide 
Olefiant gas . 
7 
7 
7 
19 
21 
31 
63 
