accounts of the scenes presented in 1799 and 1833. Extempore observatories were established at every convenient point. Watchmen were stationed, and the city bells were to be rung on the appearance of the first wandering celestial visitor. The exact night was not definitely known, but, for fear of a mistake, the 11th, 12th, and 13th were generally observed. The anxious vigils, the fruitless scannings of the sky, the disappointment, the meteors that were dimly thought to be seen,-all these were recorded in the memory of the temporary astronomers of that year.

While, however, the people of America were thus disappointed, there was enacted in England a display brilliant indeed, though inferior to the one of 1833. The staff at Greenwich Observatory counted about 8,000 meteors.

IN NOVEMBER, 1867, the long-expected shower was seen in this country, but it failed to satisfy the public anticipation. The sky was, however, illumined with shooting stars and meteors, some of which exceeded Jupiter or Venus in brilliancy.

Number of Meteors and Shooting Stars.-Prof. Newton estimates that the average number of meteors that traverse the atmosphere daily, and which are large enough to be visible to the eye on a dark, clear night, is 7,500,000; and if to these the telescopic meteors be added, the number would be increased to 400,000,000. In the space traversed by the earth, there are, on the average, in each volume the size of our globe (including its atmosphere), as many as 13,000 small bodies, each one capable of

furnishing a shooting star visible under favorable circumstances to the naked eye.

Annual Periodicity of the Star-Showers. On almost any clear night, from five to seven shooting stars may be seen per hour, but in certain months they are much more abundant. Arago names the following principal dates :

April 4-11; 17-25.
August 9-11.

October (about) 15.
November 13-14.

Origin. Aërolites, meteors, and falling stars are produced by small bodies-planets in miniature— revolving, like our earth, about the sun. Their orbits intersect the orbit of the earth, and if, at any time, they reach the point of crossing exactly with the earth, there is a collision. Their mass is so small, that the earth is not jarred any more than a railway train would be by a pebble thrown against it.

These small bodies may come near the earth and be drawn to its surface by the power of attraction; or they may sweep through the higher regions of the atmosphere, and then escape its grasp; or, finally, they may, under certain conditions, be compelled to revolve many times around the earth as satellites.

The November "meteoroids" (as these bodies are called before igniting) move at the rate of 26 miles per second in a direction nearly opposite that of the earth. They, therefore, meet our atmosphere with a relative velocity of 44 miles per second. As they sweep through the air, the friction partly arrests

their motion, and converts it into heat and light. The body thus becomes visible to us. Its size and direction determine its appearance. If very small, it is consumed in the upper regions, and leaves only the luminous trail of a shooting star. If of large size, it may sweep along at a high elevation, or plunge directly toward the ground. Becoming

highly heated in its course, it sheds a vivid light, while, unequally expanding, it explodes, throwing off large fragments which fall to the earth as aërolites, or continue their separate course as meteors. The cinders of the consumed portion rain down on us as fine meteoric dust.*

Meteoric Rings.—These little bodies, it is thought, do not generally revolve individually about the sun, but myriads of them are collected in a ring. When the earth passes through one of these floating girdles, a star-shower follows. This would account for their regular appearance at certain seasons of the year. The November meteoroids are not, like the August ones, uniformly distributed through the ring, but are principally collected in a swarm that has a period of 331 years; hence the August shower occurs quite regularly each summer, while the great November one happens only three times in a century. The orbit of the November stream extends beyond that of Uranus. The point where it crosses the earth's orbit moves forward about 50" per annum, and thus that star-shower occurs about a day later at each return. It takes three or four years for this

* Prof. Young estimates that 100 tons of meteoric matter fall upon the earth daily from outer space.

swarm to pass the node, showing that the shoal of meteoroids occupies about of its orbit. The earth

in its annual revolution about the sun is supposed to encounter several hundred of these meteoric rings.

The Physical Relation between meteoroids and comets is now generally acknowledged. The orbit of the August meteors is known to be identical with Comet III 1862 (Swift's), and that of the November 14th shower corresponds with Comet I 1866 (Tempel's). The small showers of November 24 and 27 are thought to be produced by meteors traveling in the path of the two dissevered parts of Biela's comet.

The grand problem of meteoric astronomy to-day is to identify the numerous meteoric rings, and to detect their allied comets. Being thus intimately associated, they must have a common history. Prof. Newton, the great advocate of this theory, broadly

asserts that every meteoric

stone was once a part of a comet, and every mete

oric shower consists of broken fragments of some known or unknown comet.

Radiant Point. The meteoroids are, of course, moving in parallel lines, but, by an optical illusion, they seem to radiate in all directions, the radiant point being in that part of the heavens which the earth is then approaching.* A star (u) in the blade of the sickle is the point from which the stars in the November shower radiate, while one in Perseus (7) is the radiant point of the August shower.

Height.-Herschel estimates the average height of shooting stars above the earth to be seventy-three miles at their appearance, and fifty-two at their disappearance.

Weight.-Prof. Harkness calculates that the average weight of shooting stars does not differ much from one grain.

IV. COMETS.

We come now to notice a class of bodies the most fascinating, perhaps, of any in astronomy. The suddenness with which comets flame out in the sky, the enormous dimensions of their fiery trains, the swiftness of their flight, the strange and mysterious forms they assume, their departure as unheralded as their advent,-all seem to bid defiance to law, and partake of the marvellous. Superstitious

The same illusion is seen if, looking upward, we watch snow-flakes falling during a calm. Those coming directly toward our eyes seem to be motionless, and the rest to separate from them in diverging lines. This is the effect of perspective, and the "rad. iant point" is really the "vanishing point" of the parallel lines through which the meteors are moving. See Newcomb's Astronomy, p. 399.