Note 11 — OBSERVATIONS OF THE SUN.

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.