ON CHEMISTRY. 
295 
a more rational solution of all the phenomena of heat, than that 
which is attempted to he given by the theory that, “ the earth and 
each planet belonging to this system, is furnished with the necessary 
portion of caloric , and the rays of the sun elicit the native caloric 
which is inherent in them, and occasion what is called heat.” (See 
Parkes’s Rudiments, No. 50—60, &e.) I shall not enlarge in an 
enquiry which must he referred to the action of Light —and will be 
pursued in a future paper. I do not deny that heat may lie hidden 
and masked throughout nature; but I conceive that in whatever 
state it exists, whether latent or revealed, it is an effect produced by 
the agency of the sun-beams, that have been, and continue to be, 
absorbed; and not a material essence, Sui-generis, which is integral 
with the substance of matter and independent of solar agency. 
Heat is said to radiate from the surface of the earth, and this ra¬ 
diation connected with the aqueous vapor which exists in the air, is 
the direct cause of the deposition of the dew. 
Upon this subject, in order to present some clear idea of the re¬ 
ceived theory, I must quote a few lines from the work of the late 
Doctor Wells. 
“ Heat—it is observed—is radiated by the sun to the earth, and if 
suffered to accumulate would quickly destroy the present constitu¬ 
tion of the globe. This evil is prevented by the radiation of heat 
from the earth to the heavens, during the night, when it receives 
from them little or no heat in return. The surface of the earth hav¬ 
ing thus become colder than the neighbouring air condenses a part 
of the watery vapor of the atmosphere into dew. This fluid appears 
chiefly where it is most wanted, on herbage and low plants, avoiding 
in a great measure, rocks, bare earth, and considerable masses of 
earth.” 
I must stop here to make a remark or two; for the foregoing ob¬ 
servations contain much of truth, and more that has merely a plausi¬ 
ble appearance of truth. The surface of the earth does become, at 
times colder than the air about it—this is a fact; but herein there is 
an evident departure from the ordinary law that governs the distri¬ 
bution of heat; for bodies of different degrees of temperature when 
brought into contact, tend mutually to equalise the temperature of 
each : heat will be attracted from the one, and then it may be said 
to radiate heat to the other; but the heated body will not thereby 
be so deprived of its heat as to become colder than the one which 
acted upon it: the attraction and radiation will proceed, till both 
bodies become of equal temperature. If then, the air become cooled 
by the absence of solar light, and the surface of the ground be there- 
