DISCOVERIES IN THE CELESTIAL SPACES. 309 



On considering the different stages of the development of 

 cosmical contemplation, we are able to trace from the earliest 

 ages faint indications and presentiments of the attraction of 

 masses and of centrifuo^al forces. Jacobi, in his researches on 

 the mathematical knowledge of the Greeks (unfortunately still 

 in manuscript), justly comments on "the profound considera- 

 tion of nature evinced by Anaxagoras, in whom we read with 

 astonishment a passage asserting that the moon, if its centrif- 

 ugal force ceased, would fall to the earth like a stone from a 

 sling. ""* 



I have already, when speaking of aerolites, noticed similar 

 expressions of the Clazomenian and of Diogenes of Apollonia 

 on the " cessation of the rotatory force."! Plato truly had a 

 clearer idea than Aristotle of the attractive force exercised by 

 the earth's center on all heavy masses removed from it, for the 

 Stagirite was indeed acquainted, like Hipparchus, with the 

 acceleration of falling bodies, although he did not correctly un- 

 derstand the cause. In Plato, and according to Democritus, 

 attraction is limited to bodies having an affinity for one an- 



univei'soruin, ut in uuitatem iutegritateraque suam sese conferant in 

 formam globi coeuntes. Quam affectionem credibile est etiara Soli, 

 Lunae, Cceterisque errantium fulgoribus inesse, ut ejus efficacia in ea 

 qua se repraesentant rotunditate permaneaut, quae nihilominus multis 

 raodis suos efficiuutcircuitus. Si igitur at terra facial alios, utpote se- 

 cundum centrum (mundi), necesse erit eos esse qui similiter extrinse- 

 cus iu multis apparent, in quibus invenimus annuum circuitum. Ipse 

 denique Sol medium mundi putabitur possidere, quae omnia ratio ordi- 

 nis, quo ilia sibi invicem succedunt, et mundi totius harmonia nos do- 

 cet, si modo rem ipsam ambobus (ut aiunt) oculis inspiciamus." (Co- 

 pern., De Revol. Orb. Ccel., lib. i., cap. 9, p. 7, b.) 



* Plut., De Facie in Orbe Lunce, p. 923. (Compare Ideler, Meteoro 

 logia veterum Groscorum et Romanoi-um, 1832, p. 6.) In the passage of 

 Plutarch, Anaxagoras is not named ; but that the latter applied the 

 same theory of " falling where the force of rotation had been intermit- 

 ted" to all (the material) celestial bodies, is shown in Diog. Laert., ii. 

 12, and by the many passages which I have collected (p. 122). Com- 

 pare, also, Aristot., I)e Coelo, ii., I, p. 284, a. 24, Bekker, and a remarkable 

 passage of Simplicius, p. 491, b., in the Scholia, according to the edition 

 of the Berlin Academy, where the " non-falling of heavenly bodies" is 

 noticed " when the rotatory force predominates over the actual falling 

 force or downward attraction." With these ideas, which also partially 

 belong to Empedocles and Democritus, as well as to Anaxagoras, may 

 be connected the instance adduced by Simplicius (1. c), "that water 

 in a vial is not spilled when the movement of rotation is more rapid 

 than the downward movement of the water," r^f km to Kara rov vdaro^ 



t See Cosmos, vol. i., p. 134. (Compare Letronne, Des Opiniona 

 Cosmographiqucs des Peres de VEglise, in the Revue de& Deux Mondes 

 1834, Cosmos,X. i., p. 621.) 



