Page:Popular Science Monthly Volume 5.djvu/655

Rh Kentucky State Medical Association. 1874. Pp. 262.

Experiments, showing Character and Position of Neutral Axes (Nickerson, C.E.). Pp. 26.

"Do Snakes swallow their Young?" (Goode). Pp. 12.

The Analyst, Monthly Journal of Pure and Applied Mathematics. Des Moines, Iowa. Pp. 20.

Mechanical Properties of Materials of Construction (Thurston). Pp. 28.

Assaying by the Spectroscope (Du Bois). Pp. 12.

The Mystery of Life (Cox). Pp. 32.

The Plagopterinæ and the Ichthyology of Utah (Cope). Pp. 14.

Transmission of Diseases (Hamlin). Pp. 9.

Papers chiefly Anatomical (Wilder). Pp. 94.

Transformations of the House-Fly (Packard). Pp. 14.

Geographical Variation of North American Birds (Allen). Pp. 10.

Mammals of Kansas, etc. (Allen). Pp. 23.

Statistical Atlas of the United States. Part III. Vital Statistics.

Darwinism and Language (Whitney). Pp. 30.



Coggia's Comet.—The comet which lately made such a grand display in our northern heavens was discovered by Coggia, at Marseilles, on April 17th. When first seen, the nucleus and coma together had a diameter of 100,000 miles, the comet being then 133,000,000 miles from the earth, and 153,000,000 from the sun. It travels round the sun in the same direction as the planets, but in an orbit the plane of which is very much inclined. Of all the planetary orbits, excepting those of the asteroids, that of Mercury is most oblique, having a slant of seven degrees; but the inclination of the orbit of Coggia's Comet is nearly ten times as great, being set down at 66°. Its perihelion passage, or nearest approach to the sun, occurred on July 8th, when it came within 62,000,000 miles of that orb, and it was then moving at the rate of 160,000 miles an hour. It continued to approach the earth until July 20th, coming, on that date, within 26,000,000 miles of us, when it appeared at its brightest, or, according to Prof. Parkhurst, 140 times more brilliant than when first discovered. Of its tail, the same authority says: "On June 25th the observed length of the tail was computed as 3,000,000 miles; on July 1st, 5,000,000 miles; on July 13th, 12,000,000 miles—an increase, after the first of that month, of one-twelfth per day. The tail continued, from its first appearance till the head of the comet ceased to be visible, to point from the latter directly toward the stars Beta and Gamma of the Lesser Bear. Afterward it moved slowly to the westward, so that it covered the dipper of the Greater Bear. The speed of the particles leaving the head to form the tail was estimated as over 3,000,000 miles per day. This brings the particles leaving the comet on July 4th to a distance from its head on July 24th of about 26,000,000 miles, corresponding at the latter date with the distance of the head of the comet from the earth. But, though the tail thus sweeps over sufficient space to cover the interval between the nucleus and the earth, the direction of the tail is such that it fails to reach us; its central line being distant about 4,000,000 miles, and the edge of the tail about 1,500,000 miles, from the earth."

Concerning the theory which accounts for the formation of comets' tails by a repulsive action of the sun on the matter of the nucleus. Prof. Parkhurst also writes, in the Tribune of July 23d: "The existence of a repelling force was suggested by the fact that a comet's tail, pointing eastward when the comet is east of the sun, points northward and westward as the comet itself moves around to the north and west of the sun. Yet, as there is no coherence in the tail, it is evident that no repelling force from the sun, when it is to the east of the sun, can have any tendency to bring it around to the west of the sun. The fact 