In thus putting to us from the height of their celestial apparitions so many notes of interrogation on the grandest problems of creation, comets assume to our eyes an interest incomparably greater than that with which superstition blindly surrounded them in past ages. When we reflect for a moment that a certain comet which shines before us in the sky came originally from the depths of the heavens, that it has traveled during millions of years to arrive here, and that consequently it is by millions of years that we must reckon its age if we wish to form any idea of it, we can not refrain from respecting this strange visitor as a witness of vanished eras, as an echo of the past, as the most ancient testimony which we have of the existence of matter. But what do we say? These bodies are neither old nor young. There is nothing old, nothing new--all is present. The ages of the past contemplate the ages of the future, which all work, all gravitate, all circulate, in the eternal plan. Musing, you look at the river which flows so gently at your feet, and you believe you see again the river of your childhood; but the water of to-day is not that of yesterday, it is not the same substance which you have before your eyes, and never, never shall this union of molecules, which you behold at this moment, come back there--never till the consummation of the ages! If the appearance of comets forebodes absolutely nothing as to the microscopical events of our ephemeral human history, it is not the same with the effects which might be produced by their encounter with our wandering planet. In such an encounter there is nothing impossible. No law of celestial mechanics forbids that two bodies should come into collision in their course, be broken up, pulverized, and mutually reduced to vapor. I have before described some of the tremendous outbursts seen on the surface of our sun. It is believed that in these outbursts matter is expelled, or driven forth, with such fearful violence as to send it whirling through space, never to fall back to the sun. Some meteorites may have their births thus. So also may some comets. And if all the stars are suns--huge fiery globes like our sun, and subject like him to tremendous eruptions--they too, probably, send out comets and meteorites to wander through space. Whether or no comets come into existence in any such manner, one thing seems pretty certain. Those comets which come to us from outside our system must come from some other system. And the nearest systems known are those of the stars.