Our thoughts are transported from star to star, from system to system, from region to region, in the presence of unfathomable grandeurs, in sight of celestial motions whose speed we are but just beginning properly to value, but which already surpasses all conception. The proper annual motion of the sun Alpha Centauri exceeds 188 millions of leagues per year. The proper motion of the 61st of Cygnus (second sun in the order of distances) is equivalent to 370 millions of leagues per year, or about one million of leagues per day. The star Alpha Cygni comes to us in a direct line at a speed of 500 millions of leagues per year. The proper motion of the star 1830 of Groombridge's Catalogue rises to 2,590 millions of leagues per year, which represents seven millions of leagues per day, 115,000 kilometres per hour, or 320,000 metres per second! These are minimum estimates, inasmuch as we certainly do not see perpendicularly, but obliquely, the stellar displacements thus measured. What projectiles! They are suns thousands and millions of times heavier than the Earth, launched through the unfathomable void with giddy rates of speed, revolving in immensity under the influence of the gravitation of all the stars of the universe. And these millions and thousand millions of suns, planets, clusters of stars, nebulæ, worlds in their infancy, worlds near their end, rush with equal velocity towards goals of which they are ignorant, with an energy and intensity of action before which gunpowder and dynamite are like the breath of sleeping babes. And thus everything hurries on through all eternity perhaps, without being able ever to reach the unexisting limits of infinity.... Motion, activity, light, life everywhere. Happily so, without doubt. If all these innumerable suns, planets, earths, moons, comets, were fixed and immovable, petrified kings in their eternal tombs, how much more formidable, but also more mournful, would be the aspect of such a universe! Can you imagine the whole creation stopped, benumbed, mummified? Is not such an idea unbearable? Is there not something funereal about it? What causes these motions? What maintains them? What regulates them? Universal gravitation, invisible force, which the visible universe (what we call matter) obeys. A body attracted from infinity by the Earth would attain a velocity of 11,300 metres per second; just as a body thrown from the Earth with that speed would never fall again. A body attracted by the Sun from the infinite would attain a speed of 608,000 metres; and a body thrown by the Sun with that swiftness would never return to its point of departure. Clusters of stars may give us velocities much more remarkable still, but which are explained by the theory of gravitation. A glance at a map of the proper motions of the stars is enough to make one understand the variety and grandeur of these motions. * * * * *