486 
Mr. Faraday on the 
be diminished, then it would expand, and exist of a lower 
tension ; upon the renewal of the gravitating force, either by 
approximation to the earth's surface or otherwise, the parti- 
cles would approach each other, until the elasticity of the 
whole was again equal to the force of gravity. 
Inasmuch as gases and vapours undergo no change by 
mere expansion or attenuation, which can at all disturb the 
analogy existing between them in their permanent state un- 
der ordinary circumstances, all the phenomena which have 
been assumed as occurring with the air at the limit of our 
atmosphere may, with equal propriety, be admitted with respect 
to vapour in general in similar circumstances ; for we have 
no reason for supposing that the particles of one vapour 
more than another are free from the influence of gravity, 
although the force may, and without doubt does, vary, with 
the weight and elasticity of the particles of each particular 
substance. 
It will be evident, also, that similar effects would be pro- 
duced by the force of gravity upon air or vapour of the ex- 
treme tenuity and feeble tension referred to, whatever be the 
means taken to bring it into that state ; and it is not neces- 
sary to imagine the portion of air operated upon, as taken 
from the extremity of our atmosphere, for a portion of that 
at the earth’s surface, if it could be expanded to the same 
degree by an air pump, would undergo the same changes : 
when of a certain rarity it would just balance the attraction 
of gravitation and fill the receiver with vapour ; but then, if 
half were taken out of the receiver, the remaining portion, 
in place of filling the vessel, would submit to the force of 
gravity, would contract into the lower half of the receiver, 
