COLLECTIONS AND RECOLLECTIONS; 
155 
ARTICLE XIII. 
COLLECTIONS AND RECOLLECTIONS. 
Temperature of the Sun. —That the temperature at the visi¬ 
ble surface of the sun, cannot be otherwise than very elevated, much 
more so than any artificial heat produced in our furnaces, or by 
chemical or galvanic processes, we have indications of several distinct 
kinds : 1st, From the law of decrease of radiant heat and light, 
which, being inversely as the squares of the distances, it follows, that 
the heat received on a given area, exposed it the distance of the earth, 
and on an equal area at the visible surface of the sun, must be in the 
proportion of the area of the sky, occupied by the sun’s apparent 
disc to the whole hemisphere, or as 1 to about 300,000. A far less 
intensity of solar radiation, collected in the focus of a burning glass, 
suffices to dissipate gold and platina in vapour. 2dly, From the fa¬ 
cility with which the calorific rays of the sun traverse glass, a pro¬ 
perty which is found to belong to the heat of artificial fires in the 
direct proportion of their intensity.* 3dly, From the fact, that the 
most vivid flames disappear, and the most intensely ignited solids 
appear only as black spots on the disk of the sun, when held between 
it and the eye.f From this last remark it follows, that the body of 
the sun, however dark it may appear when seen through its spots, 
may, nevertheless, be in a state of most intense ignition. It does 
not, however, follow of necessity that it must be so. The contrary is 
at least physically possible. A perfectly reflective canopy would ef¬ 
fectually defend it from the radiation of the luminous regions above 
its atmosphere, and no heat would be conducted downwards through 
a gaseous medium increasing rapidly in density. That the penum- 
bral clouds are highly reflective, the fact of their visibility in such a 
situation can leave no doubt. 
This immense escape of heat by radiation, we may also remark, will 
fully explain the constant state of tumultuous agitation in which the 
* By direct measurement with the actinometer, an instrument I have long 
employed in such enquiries, and whose indications are liable to none of those 
sources of fallacy which beset the usual modes of estimation, I find that out of 
1000 calorific solar rays, 816 penetrate a sheet of plate glass 0,12 inch thick; 
and that of 1000 rays which have passed through one such plate, 859 are capa¬ 
ble of passing through another.— Author . 
f The ball of ignited quicklime, in lieutenant Drummond’s oxy-hydrogen 
lamp, gives the nearest imitation of the solar splendour which has yet been pro¬ 
duced. The appearance of this against the sun was however as described in an 
imperfect trial, at which I was present. The experiment ought to be repeated 
under favourable circumstances.— Author. 
