shifted by different amounts and in different ways, simply because they are moving at different rates and in different directions. The scene presented to us would have been utterly untrue. Astronomy as a science could probably have had no existence in such a case. Assuredly it could have had no existence until students of the heavenly bodies had learned to accept as the first axiom of their science the doctrine that "Seeing is not believing." [Illustration: Fig 2.--Sunset at Sea.] A strange thought truly, that so active are the orbs peopling space, so swiftly do they rush onwards upon their orbits, that light, carrying its message at a rate exceeding six thousand times the velocity of the swiftest express train, would be utterly unable to give a true account of the position and movements of the celestial bodies. Fortunately light gives a true record, because the qualities of the cosmic ether are such that the message of light is transmitted hundreds of times more swiftly than the swiftest bodies in the universe travel onwards upon their orbits around each other or in space. [Illustration] II. _SPACE_ Although astronomy tells us in clearest words of the vast depths of space which surround our earth on all sides, we are not thereby enabled to realize their enormous extension. It is not merely that the unknown depths beyond the range of our most powerful telescopes are inconceivable, but that the parts of space which we can examine are on too large a scale for us to conceive their real dimensions. It is hardly going too far to say that our powers of actual conception are limited to the extent of space over which the eye _seems_ to range in the daytime. Of course in the daytime, at least in clear weather, there is one direction in which the eyesight ranges over a distance of many millions of miles,--namely, where we see the sun. But the sense of sight is not cognisant of that enormous distance, and simply presents the sun to us as a bright disc in the sky, or perhaps rather nearer to us than the sky. Even the distance of the sky itself is under-estimated. A portion of the light we receive from the sky on a clear day comes from parts of the atmosphere distant more than thirty or forty miles from us; but the eye does not recognise the fact. The blue sky seems a little farther off than the clouds, but not much; the light clouds of summer seem a little but not much farther off than the heavier clouds of a winter sky; a cloud-covered winter sky seems a little farther off than heavy rain-clouds. The actual varieties of distance among clouds of various kinds are not much more clearly discerned than the actual varieties of distance among the heavenly bodies. The estimate formed of the distance of a cloud-covered sky overhead probably amounts to little more than a mile, and it is very doubtful whether the mind presents the remotest depths of a blue sky overhead at more than two miles. Towards the