We know what air contains, and what water is composed of. There is not a mineral, not a particle of earth to which we cannot assign its composition. More than that, we can tell what is the composition of the soil of the planets, and of their satellites, those stars which roll at incalculable distances above our heads, and which we can reach only with our eyes. Science has performed this miracle, the chemical analysis of bodies which it cannot touch, and which it can only see across millions of miles in space. We have studied, classified, demonstrated all the living beings, animals and plants which people the earth. There is not an insect hidden in the grass of the fields which has not been described, which has not had its just place in creation assigned to it; there is not a blade of grass which has not been reproduced by the pencil of the naturalist. Beyond all this, science has penetrated far beyond the reach of our vision. It has invented a marvellous instrument which has unveiled an entire world to our astonished gaze, a world whose existence we never should have suspected without its aid. The world thus revealed to us is that of infinitely little things. We know that myriads of living creatures, both animals and plants, exist in a drop of water; that those creatures, in all their prodigious littleness, have a complete existence, and are as well organized as those of great size which are analogous to them, and that the physiological functions of all these imperceptible beings are fulfilled as perfectly as our own. Just as we have penetrated into the life of infinite littleness, so we have pierced the depths of celestial space, and scrutinized with our eyes the magnified image of the stars which revolve at an incalculable distance above us. The telescope shows us the surface of the moon, the depths of its ravines, and the rough serrated edges of its enormous mountains, furrowed with deep circular crevasses. We can cast our eyes over the lunar disc as if it were a distant landscape of our own globe. We can even, thanks to the magnifying powers of the telescope, form an idea of the aspect of the surfaces of those planets which are almost lost in the infinite distances of the heavens.