ON THE ABSORPTION AND RADIATION OF HEAT, 357 
of great tension, into ozone ; and the latter, at a red heat, 
may be reconverted into oxygen. Yon Babo showed that 
oxygen contracts when partially transformed into ozone, and 
assumes its original volume as soon as the ozone is recon- 
verted into oxygen. 
In order to get a clearer insight into the action of different 
bodies on radiant heat, we must for a moment consider the 
heat vibrations of the ether. If radiant heat is absorbed by 
a substance, the vibratory motion of the ether is transferred 
to the molecules of the body, ceases to exist as radiant heat, 
and the absorbing substance becomes heated. Vibrations of 
the ether which are transmitted through a substance pass 
the atoms or molecules of the latter without opposition. A 
good absorber, therefore, has a special aptitude to receive 
motion from the vibrating ether, which aptitude depends on 
the chemical and physical nature of the absorbing body. 
Elements like oxygen, hydrogen, nitrogen, and bromine are 
not so good absorbers as their compounds. If we imagine 
elements to consist of single atoms, compound bodies would 
be formed by the union of two or more atoms into one group 
or molecule, — hydrochloric acid of an atom of chlorine and 
hydrogen, water of two atoms of hydrogen and one of oxygen, 
ammonia of three atoms of hydrogen and one of nitrogen. A 
compound like ammonia, composed of four atoms, would pre- 
sent to the vibrating ether a greater surface, and therewith 
more resistance, than a single atom like chlorine ; hence, the 
latter would receive less motion from the vibrating ether, or, 
in other words, would be a worse absorber of radiant heat 
than the compound ammonia. Similar considerations would 
apply to other elements and compounds. Another influence, 
of a physical nature, must be coupled with this explanation of 
the difference in absorbing energy exhibited by various bodies. 
Vibrations are periodical motions, like the swinging to and 
fro of a pendulum. The time of one vibration is the time 
consumed whilst one movement to and fro takes place.. The 
periods of a pendulum may vary according to the length of 
the pendulum ; also the vibrations of the ether are of different 
periods, longer or shorter, according to the nature of the 
body which is their cause. The atoms of substances, be 
they solids, liquids, or gases, cannot under given conditions 
vibrate in all possible periods, but each substance has a pre- 
ference for certain periods, and will be the best absorber 
of such radiant heat which consists of vibrations of those 
periods. The rays of one source of heat would be most 
abundantly absorbed by a substance, the molecules of which 
vibrate in periods coincident with those of the source of heat. 
(To be concluded in No. XII.) 
VOL. III. — NO. XI. 2 
