Mr. Ponton has by means of a simple monochromatic photometer
ascertained that a small surface, illuminated by mean solar light, is
444 times brighter than when it is illuminated by a moderator lamp, and
1560 times brighter than when it is illuminated by a wax-candle (short
six in the lb.)--the artificial light being in both instances placed at
two inches’ distance from the illuminated surface. And three electric
lights, each equal to 520 wax-candles, will render a small surface as
bright as when it is illuminated by mean sunshine.
It is thence inferred, that a stratum occupying the entire surface of
the sphere of which the earth’s distance from the sun is the radius,
and consisting of three layers of flame, each 1/1000th of an inch
in thickness, each possessing a brightness equal to that of such an
electric light, and all three embraced within a thickness of 1/40th of
an inch, would give an amount of illumination equal in quantity and
intensity to that of the sun at the distance of 95 millions of miles
from his centre.
And were such a stratum transferred to the surface of the sun, where it
would occupy 46,275 times less area, its thickness would be increased
to 94 feet, and it would embrace 138,825 layers of flame, equal in
brightness to the electric light; but the same effect might be produced
by a stratum about nine miles in thickness, embracing 72 millions of
layers, each having only a brightness equal to that of a wax-candle.[18]