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two hundred miles a second. These motions of the stars are called their proper motions.

We have described the proper motions as so many miles per second. But owing to the enormous distance of the stars, rapid as the proper motions are in reality, they seem slow indeed when we observe them. So slow are they that if Ptolemy should come to life after his sleep of nearly eighteen hundred years, and be asked to compare the heavens as they are now with those of his time, he would not be able to see the slightest difference in the configuration of a single constellation. Even to the oldest Assyrian priests, the constellation Lyra and the star Vega looked exactly as they do to us to-day, notwithstanding the immeasurable distance by which we have approached them.

To resuscitate an inhabitant of the ancient world who would be able to perceive any change, we should have to go back four thousand years perhaps, to the time of Job, and we should have to take one of the swiftest moving stars in the heavens, Arcturus. Bringing Job to life and showing him the constellation Bootes, of which Arcturus is the brightest star, he would perceive the latter to have moved through about half of the distance in the accompanying diagram between the stars marked "1" and "2."

In considering these motions, the most natural thought to present itself is that the stars are describing vastly extended orbits around some centre, as the planets are moving round the sun, and that the motions we see are simply the motions in these orbits. But the facts do not support this view. The most refined observations yet made do not show the slightest curvature in the path of