threads fine as threads of silk, and these again resolved into finer fibres, till in more and more web-like fineness it passes beyond the reach of sight! I am speaking, however, here rather of the wonderful original, as I so well remember it, than of what my sketch or even the engraver’s skill can render. [Illustration: FIG. 19.--TYPICAL SUN SPOT OF DECEMBER, 1873. (REDUCED FROM AN ORIGINAL DRAWING BY S. P. LANGLEY.)] [Illustration: FIG. 20.--FROST CRYSTAL.] Next we have quite another “spot” belonging to another year (1873). First, there is a view (Fig. 17) of the sun’s disk with the spot on it (as it would appear in a small telescope), to show its relative size, and then a larger drawing of the spot itself (Fig. 16), on a scale of twelve thousand miles to the inch, so that the region shown to the reader’s eyes, though but a “spot” on the sun, covers an area of over one billion square miles, or more than five times the entire surface of the earth, land, and water. To help us to conceive its vastness, I have drawn in one corner the continents of North and South America on the same scale as the “spot.” Notice the evidence of solar whirlwinds and the extraordinary “plume” (Fig. 16), which is a something we have no terrestrial simile for. The appearance of the original would have been described most correctly by such incongruous images as “leaf-like” and “crystalline” and “flame-like;” and even in this inadequate sketch there may remain some faint suggestion of the appearance of its wonderful archetype, which was indeed that of a great flame leaping into spires and viewed through a window covered with frost crystals. Neither “frost” nor “flame” is really there, but we cannot avoid this seemingly unnatural union of images, which was fully justified by the marvellous thing itself. The reader must bear in mind that the whole of this was actually in motion, not merely turning with the sun’s rotation, but whirling and shifting within itself, and that the motion was in parts occasionally probably as high as fifty miles per second,--per _second_, remember, not per hour,--so that it changed under the gazer’s eyes. The hook-shaped prominence in the lower part (actually larger than the United States) broke up and disappeared in about twenty minutes, or while the writer was engaged in drawing it. The imagination is confounded in an attempt to realize to itself the true character of such a phenomenon. [Illustration: FIG. 21.--CYCLONE SPOT. (DRAWN BY FATHER SECCHI.)]