portion which is reflected sunlight, from electrical discharges between its particles. By some influence emanating from the sun, gas is emitted from the scattered swarm of meteoric particles which compose the head, and these stream out "like smoke from a locomotive" in a magnificent luminous trail. This only occurs when in the vicinity of the sun. Each time the comet comes back to the sun, it loses some of its beauty and its mass decreases—yet like a moth to a flame, it always returns. Newcomb describes the way in which a comet gradually loses itself in the following manner:
"Altogether a good idea of the operations going on in a comet may be obtained if we conceive of a nucleus (or head) to be composed of water or other volatile fluid which is boiling away under the heat of the sun, while the tail is a column of steam rising from it. We do not see the same tail of the comet all the time because the matter which makes up the tail is constantly streaming outwards and constantly being replaced by new vapor rising from the nucleus."
In the course of time, the whole comet becomes disintegrated and its pathway scattered with debris. Astronomers now look upon meteors as the remains of worn out comets, for meteoric swarms follow along the same orbits as many of the comets. When the earth crosses the orbit of a disintegrated comet, or meteoric swarm, the fragments come in contact with our atmosphere where they blaze into incandescence and are seen as shooting stars.
The Biela comet is often mentioned as furnishing the best example of comet disintegration. This comet, which was discovered in 1826, had a period of 6.6 years. In 1846, after a lapse of twenty years, it was noticed to be considerably more elongated than usual and a month later it had separated into two comets, each developing a tail of its own. Before long these twin comets had become separated by 200,000 miles. On its next return, in 1852, the two halves of Biela appeared for the second time, with the distance between them increased to 1,500,000 miles. Once
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