Tested by their reading of the phenomena on this principle, we find curious gradations between the higher and the humbler orders of minds. The vortices of Descartes, for instance, involve but a simple idea, that might have been struck out by almost any individual of a tolerably lively fancy, who had walked by the side of a winding river, and seen sticks and straws revolving in its eddies. But no fancy, however active, or no reach of mere common sense, however respectable, could have originated, or conducted to a successful conclusion, that profound contemplation into which Newton fell in the garden of Woolsthorpe, when he saw the loosened apple drop from the tree, and succeeded in demonstrating that the planets are retained in their orbits by the same law which impels a falling pebble towards the ground. So little obvious, indeed, was the Newtonian scheme, that most of the contemporary generation of philosophers,--some of them, such as Fontenelle and his brother academicians of France, men of no mean standing,--died rejecting it. And the objections of Turrettine to the motion of the earth on its axis are, we find, still more obvious than even the idea of the vortices. It does at first seem natural enough to suppose, that if the earth's surface be speeding eastwards at the rate of several hundred miles in the hour (a thousand miles at the equator), the birds which flutter over it should be somewhat in danger of being left behind; and that atoms and down flakes floating in the atmosphere in a time of calm, instead of appearing, as they often do, either in a state of rest, or moving with equal freedom in every direction, ought to be seen hurrying westwards, as if puffed by the breath of a tornado. Such an objection must for a time have appeared as just as it seems obvious, especially in one's study on a Saturday night, with much of one's lecture still to write, and the Sabbath too near to permit of verification or experiment. Fontenelle, however, though he could not get over the difficulty of conceiving how the same gravitation which made a stone fall also kept the moon in its place, fairly surmounted that which puzzled Turrettine; and in his "Plurality of Worlds,"--a publication of the same age as the "Compendium Theologica,"--he makes his Marchioness surmount it too. "'But I have a difficulty to solve,' he represents the lady as saying, 'and you must be serious. As the earth moves, the air changes every moment; so we breathe the air of another country.' 'Not at all,' replied I; 'for the air which encompasses the earth follows with us, and turns with us. Have you not seen the labors of the silkworm? The shell or cocoon which it weaves around itself with so much art is of a down very loose and soft; and so the earth, which is solid, is covered, from the surface twenty leagues upwards, with a kind of down, which is the air, and, like the shell of the silkworm, turns along with it.'" Even