Page:Popular Science Monthly Volume 42.djvu/563

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the other, according as the body which contained dark lines in its spectrum was approaching the earth or receding from it.

After this very brief statement of general principles, we can now refer to the observations that have already been made with regard to the spectrum of the present new star, observations unique in astronomical history, and of the highest importance and interest. It has been found to consist of both light and dark lines. The fact that pairs of bright and dark lines are seen proves that two bodies are in question. If we suppose two swarms of meteors colliding in space, the spectrum can be easily explained on this assumption in the light of the general principles referred to above. Further, the thickness of the lines tends to show that each one is produced by a large number of small incandescent masses moving at different velocities, rather than by one large one. The motion necessary to produce the doubling of these lines has been estimated, and the relative velocity of the two swarms has been put down as more than five hundred miles per second!

If the photographs should continue to show the same relative positions of the bright and dark lines, the observations would prove that this relative motion is not produced by the revolution of one body round another, but that a dense swarm of meteorites is moving toward the earth with a high velocity, and passing through another receding one of less density.

It will be seen that the observations harmonize well with the hypothesis that has been advanced on much less definite evidence; but this is not the only instance we can give of the grip that modern science has on large classes of phenomena which were supposed to be beyond the reach of man. The lines that have been photographed in the spectrum of this star are all such as could have been predicted with our knowledge of new stars.

As an instance of the advanced stage at which astro-physical science has arrived, we may say that, if we had no observations of new stars other than those already recorded of the present one, their whole theory could be obtained by induction. This may seem a "sweeping statement," but it is nevertheless true, for since many so-called "stars" are now known not to be "stars" like our sun, but simply clouds of meteoritic bodies clashing together, and since we know approximately the sequence of changes through which the spectra of these stars pass as their temperature is first increased and then reduced, each spectrum indicates the complexity of each swarm.

We have already seen that the doubling of the bright and dark lines indicates that we are dealing with two swarms in the present instance, one approaching and the other receding; we now learn that the condensation at which each of these swarms

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