THE BIRTH AND DEATH OF WORLDS 403 



celebrated Natural History, cherished companion of the mind 

 of youth. Let us take note of the facts upon which he had 

 to build. 



The earliest observers, to whom the truth had become clear 

 that the planets travel in circles, must have likewise noted that 

 they all travel the same way. Some among them may have 

 noted that the circling path of the moon is in the same direc- 

 tion. When the heliocentric ideas of Aristarchus had been 

 established, it was found that the earth was journeying the 

 way of the rest. All this could hardly be mere coincidence. 



Then came the discovery of the various satellites first of 

 Jupiter, then of Saturn. All of these revolve about their 

 central orbs in the same manner as the moon. Finally, it was 

 observed that the earth's revolution upon its own axis was in 

 the same direction. So it was found were the revolutions of 

 all the other planets, and finally that of the sun, as one by one 

 they were revealed by the telescope. 



Putting all these motions together, Bernouilli had calculated 

 that, in the theory of chance, it was millions to one that this 

 could not be due to mere hazard. Whatever force, whatever 

 power, had impressed this especial direction of motion upon 

 one had evidently acted in the same way upon all. 



Moreover, there was another curious fact. If one could 

 take up a point of observation somewhat distant from the 

 outermost rim of the solar system, he would observe that the 

 whole of the planetary motions take place within a thin plane. 

 If we project through the intervening spaces the disk which 

 the ancients had named the ecliptic, or plane of eclipses, it is 

 noted that none of the planetary orbits are inclined very much 

 above or below this median line. Altogether, the steepest 

 of the inclinations, at least in Buff on' s time, did not exceed 

 one-seventeenth part of the sphere of the heavens. This could 

 be as little the outcome of chance as the common direction of 

 movement. What was the determining cause of this striking 

 uniformity ? 



The mind of Buffon found a hint in the calculations of 

 Newton as to the relative mass of the planets and the sun. 

 Newton had computed that the mass of the known planets 

 and satellites put together would not equal the 65oth part of 

 the mass of the sun ; we know now, of course, that even with 



