The Tail of A Comet

1895

Its Ever Changing Mass and Why It Flees From the Sun.

The tail of a comet is not formed of the same particles which composed it yesterday or even an hour or a moment ago. It is constantly being renewed at the expense of the nucleus. As the long stream of black smoke from the neighboring factory or mill is being continually renewed by fresh particles of carbon released by the combustion going on in the furnace below, so is the wonderful luminous train of cometery bodies being constantly replenished by particles flying from, of rather driven from, the nucleus by the intense heat of the sun.

Then, again, how infinitely small and how intensely luminous must these particles that go to make up the tail of a comet be! This thought is suggested by the fact that it has been proved that in some cases the nucleus of comets which are only a few hundred miles in diameter will have enormous fanlike tails stretching across space for a distance exceeding 200,000,000 miles and having a bulk exceeding that of the sun by more than 10,000 times! Professor E. E. Barnard beautifully illustrates the formation of a comet's tail by "supposing" thus: "Suppose, for example, that the nucleus of a comet is composed of ice. Then suppose the heat of the sun to be so intense as to rapidly melt that portion of the ice globe exposed to the action of its rays, which are strong enough to immediately convert it into vapor, which ascends toward the sun.

"Imagine now a fierce wind blowing out from the sun, causing the vapor which meets it to be whirled out into space behind the comet. This will clearly illustrate the theory of the formation of a comet's tail, only that the nucleus of the comet is not ice and the vapor is not water vapor; neither is the force which drives it away from the sun a fierce wind."

The unknown force hinted at by the astronomer above quoted readily explains why a comet's tail, as a rule, points in an opposite direction to the sun. The Russian astronomer, Brediechen, distinguishes three different types of cometary tails — those composed of particles having the specific gravity of hydrogen, those having the specific gravity of hydocarbon gas, and a third class having all the peculiarities of an equal mixture of hydrogen and iron vapor. — St. Louis Republic.