CONSTITUTION OF COMETS.

Wairarapa Age, Volume XXXII, Issue 3189, 14 May 1909, Page 7

CONSTITUTION OF COMETS.

The nature of comets was long in doubt, and even to-day their physical characteristics are not fully understood. They are certainly formed of gravitational matter, since they move in orbits which are subject to the «*ame,laws as of the planets. But they also appear to be acted upon by powerful "repulsive forces" emanating from the sun to which is due the remarkable phenomenon of cometary tails. At first it was supposed that a comet and its tail consisted of what we know as solid matter. But the observed facts are quite iriconsiste.it with this theory. ; A comet'a tail, which stretches for many millions of miles, .is always directed away from the sun, and when tho comet swings rapidly round the sun the whole of this tail follows its motion in such a kind of manner with which we are acquainted. The probability is that these tails consist of. highly rarefied matter thrown oT from the-comet under the influence of repulsive force emanating from the sun which is probably/electrical in its nature. The degree of rarefaction of the matter composing thise tails is probably greater than that of any vacuum which we .can prouduce in our laboratories, and, its luminosity is due to similar causes .to those which produce the glow in a vacuum tube through which an electric current is passed. The extreme tenuity of comets is proved by various facts, such as that the earth is known tu have parsed right through the tail of a comet without any apparent effect, that the close approach of a comet to a planet causes no apparent alteration of the planet's motion, (? and that small stars can be seen shining . brightly right through a comet as much 'as

100.C1.00 miles in diameter. Perhaps thera is not much exaggeration in the statement once made by a wellknown astronomer that the whole material of a comet stretching halfway across the visible heavens, if properly compressed, could be placed in o hat box. The old fear that the earth might suddenly be annihilated by a comet striking it is thoroughly dispelled by modern investigation, which leads us to believe that the worst results of such an encounter would be an extremely beautiful display of shooting stars. —W. E. Garrett Fisher, in "Harmsworth Self-Educator."