THE FIRST IDEAS OF GRAVITATION 123 



it did not diminish, highsoever as they could go ; indeed the 

 greater the height from which a body falls, the longer the time 

 it is falling, the swifter the speed of the fall. 



Does this force extend then indefinitely up into the sky ? 

 What, for example, is the meaning of this curious connection 

 which seems to subsist between the moon and the tides, which 

 Poseidonius and Seleucus have studied so attentively. Does 

 the moon pull the waters of the sea ? And if so, is this pulling 

 force between moon and earth reciprocal ? Why, for example, 

 does the moon move round the earth in a circle ? Why does 

 it not fly off into space ? What holds it ? Is this same 

 attractive force, acting towards the earth's centre, constantly 

 pulling the moon downwards towards the earth, as an arrow 

 shot into the air falls back again when its force is spent ? 



There were surely minds before which this far-reaching con- 

 ception floated ; in foremost line that rich, proud Anaxagoras, 

 whom Pericles saved from the vengeance of the Athenians for 

 his cold disdain of their rabble of gods. Humboldt quotes 

 Jacobi as commenting on " the profound consideration of nature 

 evinced by Anaxagoras, in whom we read with astonishment a 

 passage, that the moon, if its centrifugal force ceased, would 

 fall to the earth like a stone from a sling. 1 ' It was this 

 same Anaxagoras who pictured " the ether surrounding the 

 earth as a fiery substance which by the power of its rotation 

 tears rocks from the earth, inflames them and converts them 

 into stars," l a curious antithesis of present-day ideas of 

 meteorites. It was doubtless in following out his idea that 

 Anaxagoras came to regard the sun as a colossal body of red- 

 hot iron. 



In Diogenes of Apollonia, in Democritus, in Empedocles, in 

 Plato and others, are to be found notions more or less vague, 

 of this same force of attraction. It seems almost to have been 

 common property. In Plutarch, in his Life of Lysander, is 

 to be found a curious passage regarding falling stars, " which 

 are," he says, " according to the notions of some of the 

 physicists, not eruptions of the ethereal fire extinguished in 

 the air immediately after their ignition (!), but these meteors 

 are rather a falling of celestial bodies, which, in consequence of 

 a certain intermission in the rotatory force, have been hurled 

 down." 



1 Plutarch, De Placitis Philosophorum. 



