And all motions which would in the remotest degree affect the shapes of constellations, must be sideway motions. Those line-of-sight motions, of which the spectroscope alone tells us, could never have been discovered by simple observation of the sky. Until the new method came to light we had no means whatever of perceiving such movements among the stars. Suppose you are looking at two men in the distance, upon a wide, flat plain. One of the two is walking very slowly _across_ your line of vision. The second man is moving very slowly straight _towards_ you. If you watch with care you may find out both the movements. The sideway walking will be apparent first and most easily, because, as the man moves, he has constantly a fresh part of the horizon behind him. But in time the advance of the second man towards you will also become apparent; for although he is seen still against precisely the same spot on the horizon, he slowly occupies a larger spot on the retina of your eye,--in other words, he seems to grow bigger. And that, as you know from long experience, can only mean increasing nearness. If a star seemed to grow larger as it drew nearer, we should then be able to perceive that movement also. But no star in the sky ever does seem to grow any larger. Every star is to us but one point of light. It may be rushing towards us at an enormous rate of speed, yet still as a single point it remains, always at the same point in our sky. Therefore we have no chance of perceiving its movement; or rather, we _had_ no chance until the discovery of this new method. In fact, the very nearest known star is at so enormous a distance that, supposing it to be coming towards us at the rate of one hundred miles each second, it would still gain, in the course of a century, only one-fortieth part more of brightness than it has now. It would not increase at all in apparent size. When we leave behind us the thought of starry motions, as we faintly detect them at this great distance, and picture to ourselves the actual far-off whirl of all those glorious suns, the effect upon the mind is overwhelming. Stars are found to be rushing hither and thither, at every degree of speed, in every imaginable direction: stars to right, and stars to left; stars towards us, and stars away from us; stars alone, and stars in company,--all this, and more, deciphered out of the tiny gleam of quivering light, which streams through the vast abyss of space from each distant orb to earth. So real star-motions were known--first, through telescopic observation; secondly, through spectroscopic observation; and now, lastly, photography has stepped in, bringing with it much increase of exactitude.