To the article at pp. 59-60 should be added the result obtained by Dr.
Woods of Parsonstown, and communicated to the _Philosophical Magazine_
for July 1854. Dr. Woods, from photographic experiment, has no doubt
that the light from the centre of flame acts more energetically than
that from the edge on a surface capable of receiving its impression;
and that light from a luminous solid body acts equally powerfully from
its centre or its edges: wherefore Dr. Woods concludes that, as the
sun affects a sensitive plate similarly with flame, it is probable its
light-producing portion is of a similar nature.
_Note to_ “IS THE HEAT OF THE SUN DECREASING?” _at page 65_.--Dr.
Vaughan of Cincinnati has stated to the British Association:
“From a comparison of the relative intensity of solar, lunar,
and artificial light, as determined by Euler and Wollaston, it
appears that the rays of the sun have an illuminating power
equal to that of 14,000 candles at a distance of one foot, or
of 3500,000000,000000,000000,000000 candles at a distance of
95,000,000 miles. It follows that the amount of light which
flows from the solar orb could be scarcely produced by the daily
combustion of 200 globes of tallow, each equal to the earth in
magnitude. A sphere of combustible matter much larger than the
sun itself should be consumed every ten years in maintaining its
wonderful brilliancy; and its atmosphere, if pure oxygen, would be
expended before a few days in supporting so great a conflagration.
An illumination on so vast a scale could be kept up only by the
inexhaustible magazine of ether disseminated through space, and
ever ready to manifest its luciferous properties on large spheres,
whose attraction renders it sufficiently dense for the play of
chemical affinity. Accordingly suns derive the power of shedding
perpetual light, not from their chemical constitution, but from
their immense mass and their superior attractive power.”