460 On the received Theory of Heat. 
the lower foramen, showing the rounded edges of the slit, which 
consequently leave a slight channel along the tooth. 
I, IX, magnified representations of sections of the fangs of an 
unknown species of serpent, which have exactly the same form 
as those of the rattle-snake. 
I, is a section of a young fang taken about the middle: in this 
stage of growth, the cavity which contains the pulp almost en- 
tirely surrounds the poison tube; and the edges of the depres- 
sion which form the suture are seen to be angular, and present 
so large a surface to each other, that the suture is completely 
filled up even in this early stage of growth. 
Kx, is a section of a full-grown fang of the same species of ser- 
pent at the same part as the preceding. Here the cavity of the 
pulp is seen greatly contracted from the more advanced stage of 
growth. 
LXX. On the received Theory of Heat. By A Correspon- 
DENT. 
To Mr. Tilloch. 
Sir, — Ix addition to my hasty remarks (in your October Num- 
ber) I think that heat is only the effect of a decomposing prin- 
ciple circulated from, or sympathetic with, the sun, because of 
its peculiar activity when immediately under it, and its indolence 
when out of its presence, except when collected in the form of 
combustion, electricity, galvanism, or lightning, &c. It then 
shows an appearance corresponding with the matter it is com- 
pounded with, and disorganizes any substance in proportion to 
the purity, quantity and rapidity of its application to it. Com- 
bustion is perhaps maintained by the flowing in of the decom- 
posing principle from the adjoining air, and lightning an acci- 
dental mass bursting to a natural distribution, and violently dis- 
uniting the component parts of the atmosphere, upon whose Junc- 
tion meteoric stones may be formed from the half-melted mate- 
rials. On the equator this influence is the most regular and ef- 
fective—raising befor the sun a prodigious increase of atmosphere 
out of earth, water, &c. forcing by expansion a current of air 
from it, which being resisted (in degree) by a more dense atmo- 
sphere, produces a ‘Teaction upon the surface of the earth, and 
thereby a constant revolution towards the sun. If elementary 
heat. was the cause of this, T think our atmosphere would be 
wholly condensed before it reached the icy regions; its heat would 
be entirely withdrawn, and the matter it is composed of descend 
to the earth in particular latitudes. In the case of insensible 
perspiration in plants and animals, we perceive a decomposition 
of 
