Page:The Solar System - Six Lectures - Lowell.djvu/30



the lingering scarf of light left when the body itself has eluded us, but no sound is heard, and nothing reaches the earth. The visitants come, too, in swarms. They have their times and seasons. Different nights of the year are consecrate to special flights; and the successive years bring back the same flights like birds that honk overhead at the same recurrent season of the year.

Such regularity has caused them to be noted and studied, and we have now a score of well-recognized congeries of shooting-stars or meteoric streams, known, for example, as the Leonids, the Perseids, the Andromedes. Each swarm has its radiant or perspective point from which all its members seem to come. From this radiant it derives its name, the Leonids seeming to come from a point in the constellation Leo, the Orionids from the constellation of Orion, and the Lyrids from the Lyre.

Each of these swarms enters our atmosphere with cosmic speed, all the shooting-stars of one swarm travelling at the same rate; but each swarm has its own distinctive velocity. The Andromedes move relatively slowly,—eleven miles a second,—and are reddish. They overtake us; this accounts for their sluggishness, and their sluggishness