Again, some astronomers thought that such stars as could be perceived to move most rapidly in the course of years would be the most hopeful objects to attack, since the more rapid movement might be supposed to mean greater nearness, and so greater ease of measurement. But some stars, seen to move rapidly, are now known to be more distant than others which are seen to move more sluggishly. So neither of these two rules could altogether be depended on; yet both were, on the whole, the best that could be followed, either separately or together. The star 61 Cygni is not one of the brighter stars, but it is one of those stars which can be seen to travel most quickly across the sky in the course of a century. Therefore it was selected for a trial; and that trial was the first to meet with success. For 61 Cygni was found to have an apparent parallax; in other words, its tiny seeming journey through the year, caused by our earth’s great journey round the sun, could be detected. Small as the star-motion was, it might, through careful measurement, be perceived. And, in consequence, the distance of the star from earth could be measured. Not measured with anything like such exactitude as the measurements of sun-distance, but with enough to give a fair general notion of star-distance. One success was speedily followed by others. By a few others,--not by many. Among the thousands of stars which can be seen by the naked eye, one here and one there responded faintly to the efforts made. One here and one there was found to stir slightly in the sky, when viewed from earth’s summer and winter positions, or from her spring and autumn positions, in her yearly pathway round the sun. It was a very, very delicate stir on the part of the star. Somewhat like the difference in position which you might see in a penny a few miles off, if you looked at it first out of one window and then out of another window in the same house. You may picture the penny as radiantly bright, shining through pitch darkness; and you may picture yourself as looking at it through a telescope. But even so, the apparent change of position in the penny, viewed thus, would be exceedingly minute, and exceedingly difficult to see. There are two ways of noting this little seeming movement on the part of a star in the sky. Either its precise place in the sky may be observed--its exact position, as in a map of the heavens--or else its place may be noted as compared with another more distant star, near to it in the sky, though really far beyond. Parallax, if visible, would make it alter its precise place in the sky. Parallax, if visible, would bring it nearer to or farther from any other star more distant than itself from earth. The more distant star would have a much smaller parallax--probably so small as to be invisible to us--and so it would do nicely for a “comparison star.” The first of these methods was the first tried; and the second was the first successful.