1833.] Attraction and Repulsion. 507 
former however may arise from the great attraction of clay for 
water; which only the greatest heat can drive off; and of the latter 
the usual explanation, that it arises from the loss of polarity, which 
the particles had assumed, appears quite satisfactory. If these be 
objections, they apply, at least as much, to the theory of vibration ; 
for even were it possible, that an increase of vibration in particles 
could give rise to expansion, these experiments would show increase of 
vibration attended with contraction. 
6. The combinations and decompositions often effected by the rays 
of the sun, are certainly not always conformable to the laws of this 
doctrine of heat; but neither are they to any other doctrine. 
7. It has been objected to heat being the cause of elasticity in gases; 
that this force varies as the density, although in the condensation of 
gases, much heat is evolved. But this experiment only shews, that, 
in the condensation of gases, part of their heat is evolved; which if 
it remained would cause their elasticity to vary in a higher ratio than 
that of the density. 
8. Lastly, it has been objected to the materiality of heat, that 
notwithstanding the most accurate experiments have been made, it has 
always been found impossible to ascertain, that it has weight. 
This objection however is not valid, since it has neither been possible 
to weigh light, though few will doubt its materiality, or the materiality 
of some ether in which its phenomena are seated; which hypothesis 
merely removes the difficulty of its materiality one step farther. It 
has also been very justly remarked by.a great philosopher, whom I 
have already quoted, that if this etherial fluid be supposed as much 
lighter than hydrogen gas, as the latter is than the metal platinum, 
it could not probably be ascertained to have weight by any means 
which are known*, 
The above are most of the facts, which are considered as objections to 
the material doctrine of heat, many of which may be sufficiently explained. 
~ Much more may be said in support of the doctrine. 
As the materiality of light can scarcely be questioned, since Sir 
Isaac Newron has so ably argued in proof of it, and since on it he has 
built his system of optics, which could not be founded on any other 
doctrine, the striking analogy between it and heat, must strongly 
point out the materiality of the latter. Heat, like light, is radiated 
from the sun ; like light, it travels with exceeding velocity ; like light, 
it is radiated by many bodies, is reflected, is refracted ; and according 
to Berarp, is sometimes, like light, polarized. From analogy so strik~ 
* Sir H. Davy’s Elements of Chemical Philosophy, p. 97. 
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