Page:The Scientific Monthly vol. 3.djvu/536

 THE .SCIENTIFIC MONTHLY

��Wta. 3. IIallei's Couet. Mat 1. 1910; bead and bcglDtilDg of tall.

ing mass of hazy, nebulous matter. The head is eometimes circular in outline, more frequently elliptical or nearly so, but again it is oval on the edge facing the sun and it merges insensibly into the tail on the side opposite the sun (Figs. 3, 4 and 5). The sizes of comet heads vary enormously. One loss than 10,000 miles in diameter would be most unusual and generally would escape di,'<covery. The head of the great comet of 1811 was at one time more than a million miles in diameter. The head of the great comet of 188S, which many of us

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