Page:Popular Science Monthly Volume 87.djvu/225

Rh the next approach to the Sun carries the scattering process a step further. Repeated returns to the Sun dissipate the individual constituents of the comet more widely. The intensity of the comet's light is reduced, and eventually it becomes too faint for discovery and observation. There is little room to doubt that this process is responsible for the total disappearance of several periodic comets.

The argument is strongly supported by the meteor streams. It is well known that on certain nights of the year we see an unusually large number of meteors, which come from certain definite directions in space. These meteors have been extensively observed and their orbits have been computed. The illustration shows the orbits of four such swarms.

They intersect the Earth's orbit at certain computed points. We pass through those points on certain nights of the year and the meteoric materials moving in the one orbit collide with the Earth in the other orbit. Now, it has been shown that the orbits of these four meteor streams and of one other stream are the orbits of five periodic comets which have disappeared from sight. Clearly, the cometary materials had been gradually scattered by the disintegrating effect of the Sun's attraction, and the separate particles were compelled to move in orbits differing slightly from each other, and from the recognized orbits of the comets. The meteoric collisions with the Earth are such as to show that we are dealing with widely separated small masses moving in orbits nearly identical with each other.

In the case of these five swarms there is certainly a close connection between meteors and comets. Whether all meteoric matter has come from the disintegration of comets can not be answered now. We can