EADIATION or HEAT BY G-ASEOUS MATTEE. 
81 
air oscillate, but the ether does not swell. We have here a definite picture before the 
mind’s eye, which, if the theory of an ether be true, is as certain as any conclusion of 
mathematics, and would hardly be rendered more certain if the physical vision were so 
sharpened as to be able to see the oscillating atom and the fluid in which it swings. I 
write thus strongly and definitely lest it should be imagined that I am dealing in vague 
conjectures in connexion with this subject. If I am vague, the mechanical theory of an 
ether must in reality bear the reproach. So far, however, from having a reproach to 
bear, the whole body of facts is in complete harmony -with this theory. 
Further, if, as all the facts declare, radiation and absorption are complementary acts, 
the one consisting in communication, the other in reception, and the one being strictly 
proportional to the other, no coincidence in period between the vibrations of a radiating 
body and those of oxygen, hydrogen, or air, could make any one of these substances a 
good absorber. The form of the atom, or some other attribute than its period of oscil- 
lation, must enter into the question of absorption. It is physically incapacitated from 
communicating motion, and hence in an equal degree incapacitated from accepting 
motion. The neutrality of elementary gases in the experiments on absorption already 
recorded does not arise from my accidentally choosing a source of heat whose periods do 
not sjTichronise with those of the gas ; for however they might spichronise, the gas would 
still be a bad absorber. Even when the motion which then' own absorbent power does 
not enable them to take up is mechanically imparted, or is communicated to them by 
contact, they are still incompetent to expend it upon the ether, which accepts all vibra- 
tions ahke *. 
§ 9 . 
Scents and effluvia generally have long excited the attention of observant men, and 
they have formed favourite illustrations regarding the dhisibility of matter. Several 
chapters in the works of the celebrated Egbert Boyle are devoted to this subject, and 
eminent men in all countries have speculated more or less upon the extraordinary 
tenuity of the matter which is competent to produce sensible efiects upon our organs of 
smell. Such a subject would of course in itself form a wide inquiry, which it is quite 
out of my power to develope at present. I think, however, that the aj^paratus which we 
have thus far made use of enables us to deal with the question in a manner hitherto 
unattainable. 
A number of diy aromatic plants f were obtained from Covent Garden, the leaves and 
flowers of which were stuffed into glass tubes 18 inches long and a quarter of an inch 
in diameter. By means of my second air-pump, a current of dry air was first passed 
* I can hardly imagine the bands in the spectra of metallic compounds to be produced by the vibration 
of the compound atom. All my experiments show tlie vast influence of chemical union on the rate of oscil- 
lation ; the metal itself and the compound of that metal could hardly, in my opinion, oscillate alike. Hence 
I infer that decomposition has occurred when the bright and constant spectral bauds are seen. — June 20th. 
t I mean “ dry” in the common acceptation of the term. They were not green, but withered ; doubtless, 
strictly speaking, they contained aqueous vapour. 
ilDCCCLXII. M 
