Any one who happens to gaze at the sky for a short time on a clear night is pretty certain to be rewarded with a view of what is popularly known as a "shooting star." Such an object, however, is not a star at all, but has received its appellation from an analogy; for the phenomenon gives to the inexperienced in these matters an impression as if one of the many points of light, which glitter in the vaulted heaven, had suddenly become loosened from its place, and was falling towards the earth. In its passage across the sky the moving object leaves behind a trail of light which usually lasts for a few moments. Shooting stars, or meteors, as they are technically termed, are for the most part very small bodies, perhaps no larger than peas or pebbles, which, dashing towards our earth from space beyond, are heated to a white heat, and reduced to powder by the friction resulting from their rapid passage into our atmosphere. This they enter at various degrees of speed, in some cases so great as 45 miles a second. The speed, of course, will depend greatly upon whether the earth and the meteors are rushing towards each other, or whether the latter are merely overtaking the earth. In the first of these cases the meteors will naturally collide with the atmosphere with great force; in the other case they will plainly come into it with much less rapidity. As has been already stated, it is from observations of such bodies that we are enabled to estimate, though very imperfectly, the height at which the air around our globe practically ceases, and this height is imagined to be somewhere about 100 miles. Fortunate, indeed, is it for us that there is a goodly layer of atmosphere over our heads, for, were this not so, these visitors from space would strike upon the surface of our earth night and day, and render existence still more unendurable than many persons choose to consider it. To what a bombardment must the moon be continually subject, destitute as she is of such an atmospheric shield! It is only in the moment of their dissolution that we really learn anything about meteors, for these bodies are much too small to be seen before they enter our atmosphere. The débris arising from their destruction is wafted over the earth, and, settling down eventually upon its surface, goes to augment the accumulation of that humble domestic commodity which men call dust. This continual addition of material tends, of course, to increase the mass of the earth, though the effect thus produced will be on an exceedingly small scale.