ance, which would explain
why solar light is not diffused through space, and thus account for
nocturnal darkness.

The combination of glasses which enabled me to inspect the above details
may be stated briefly thus: In the place of my astronomic eyepiece, I
use an elongator (obtainable of opticians) to increase the power. Into
this I place my terrestrial tube, retaining only the field glasses, and
using a microscopic eyepiece of seven eighths of an inch in diameter.
Over this I slide a tube containing my colored glasses, one dark blue
and two dark green, placed at the outer end of the sliding tube, one and
a half inches from the eyeglass. The colored glasses are three quarters
of an inch in diameter, and the aperture next the eye in diameter half
an inch. The power which I usually employ magnifies but one hundred and
fifty diameters; and I use the entire aperture of my object glass. This
combination of colored glasses gives a clear dead white to the sun, the
most desirable for distinct vision, as all shaded portions, such as
spots, however minute, and their underlying dusky penumbra, are thus
brought into strong contrasts.

FOOTNOTES:

[11] Imagine an immense sphere enclosed within two contiguous and
equally thin envelopes, and yet sufficiently thick to show their edges
distinctly when broken; the outer, a photosphere, having an intensely
bright surface, and the inner, or penumbra, of a dull gray surface;
while the enclosed hollow space is all dark, with the exception of an
occasional fleecy cloud, floating within, and contiguous to the inner
envelope. Now remove a large irregular piece from the outer, and a
smaller piece from the inner envelope, and you have an exact idea of the
appearance of a spot; contrasting the comparative brilliancy of the
photosphere with the penumbra; their relative thickness; the intense
blackness within, and occasional cloud stratum floating beneath the
opening, as seen, under the most favorable circumstances, with a good
telescope.

FOOTNOTES:

[12] The Nasmyth willow-leaf appearance, I think, is either the result
of imperfect vision, defective instruments, or unfavorable state of the
air, distorting the unvarying result of my observations, as above
described, which have been a thousand times repeated in our clearer
atmosphere, both on the coast and interior mountain regions. My
observation of a general pore-like character, over the whole surface of
the photosphere of the sun, is, I t