226 On the Nature and Conftruétion 
not appear that they had any other foundation for their af- 
fertions than mere opinion and vague furmife; but now Ff 
think myfelf authowifed, «pon affronomical principles, to pro- 
pofe the fun as an inhabitable world; and am perfuaded that 
the foregoing obfervations, with the conclufions I have drawn 
from them, are fully fufficient to anfwer every objection that 
may be made againft it. 
It may, however, not be amifs to remove a certain diffi- 
culty, which arifes from the effect of the fun’s rays upon our 
globe. The heat which is here, at the diftance of 95 millions 
of miles, produced by thefe rays, is fo confiderable, that it 
may be objected, that the furface of the globe of the fun it~ 
felf muft be feorched up beyond all conception, . 
This may be very fubftantially anfwered by many proofs 
drawn from natural philofophy, which thew that heat is pro- 
duced by the fun’s rays only when they act upon a calorific 
medium; they are the caufe of the production of heat, by 
uniting with the matter of fire which is contained in the fub- 
{tances that are heated; as the collifion of flint and fteel will 
inflame a magazine of gunpowder, by putting all the latent 
fire it contains into action. But an inftance or two of the 
manner in which the folar rays produce their effect, will 
bring this home to our moft common experience. 
On the tops of mountains of a fufficient height, at an alti- 
tude where clouds can very feldom reach to fhelter them from 
the direct rays of the fun, we always find regions of ice and 
fnow. Now, if the folar rays themfelves conveyed all the 
heat we find on this globe, it ought to be hatteft where their 
courfe is leaft interrupted. . Again, our aéronauts all confirm 
the coldnefs of the upper regions of the atmofphere; and 
fince, therefore, even on our earth, the heat of any fituation 
depends upon the aptnefs of the medium to yield to the im- 
preffion of the folar rays, we have only to admit, that, on 
the fun itfelf, the elaftic fluids composing its atmofphere, and 
the matter on its furface, are of fuch a nature as not to be 
capable of any exceffive affection from its own rays: and, in- 
deed, this feems to be proved by the copious emiflion of 
them; for if the elaftic fluids of the atmofphere, or the mat- 
ter contained on the furface of the fun, were of {uch a nature 
5 ; as 
niece 
