332 THIRD EXPLANATION 



keep time together [s'accordenf]. Now that may happen 

 in three ways. The first way consists in the mutual in- 

 fluence of each clock upon the other ; the second, in the 

 care of a man who looks after them ; the third, in their 

 own accuracy. The first way, that of influence, was 

 ascertained on trial by the late M. Huygens 4 , to his great 

 astonishment. He attached two large pendulums to the 

 same piece of wood. The continual swinging of these 

 pendulums imparted similar vibrations to the particles of 

 the wood ; but as these different vibrations could not 



the motion occurs, the will wills it, without any causality or 

 influence [influxes] of the one upon the other ; as in the case of 

 two clocks which are carefully adjusted together to the daily 

 course of the sun, as often as the one strikes and tells us the 

 hours, the other strikes in the same way and indicates the hours, 

 and that apart from any causality, by which the one might produce 

 this effect in the other, but solely on account of the connexion 

 which comes from the fact that both were made by the same 

 art and with similar workmanship. Thus, for example, the 

 motion of the tongue accompanies our volition to speak, and this 

 volition accompanies that motion : and the motion does not depend 

 upon the volition, nor the volition upon the motion, but both 

 depend upon the same Supreme Artificer, who has so wonderfully 

 connected and bound them together.' Ethica, Tract. I. cap. 2, 2, 

 note 19 ; Land's ed., vol. iii. p. 2-1 1. Cf. ibid, note 48 ; Land, iii. 220. 

 Cf. also Introduction, Part ii. p. 43. 



* Christian Huygens (1629-1695) was a mathematician, phy- 

 sicist and astronomer, who lived for the most part in Holland, 

 where he was born, and in France, where Leibniz, coming to 

 Paris in 1672, met him. Anticipating the revocation of the Edict 

 of Nantes, the Protestant Huygens left Paris in 1681 and returned 

 to Holland, but he continued to correspond with Leibniz on 

 mathematical subjects. In 1673 Huygens published his great 

 work Horologium OscillatQrium, sive de motu pendulorum ad horologia 

 adaptatOj in which he gave a full account of a discovery he had 

 made in 1656, that of the pendulum clock. Among the other 

 great works of Huygens were discoveries in connexion with the 

 astronomy of the planets, the undulatory theory of light, and 

 the use of spiral springs for regulating the balances of watches. 

 Leibniz frequently acknowledges his great indebtedness to 

 Huygens in regard to mathematics, and in July, 1695, he writes 

 to Nicaise : ' Nothing can equal the loss of the incomparable 

 M. Huygens. Most certainly he ought to be named immediately 

 after Galileo and Descartes. He might still have given us great 

 light upon nature' (G. ii. 552). But elsewhere he says that 

 ' M. Huygens had no taste for metaphysics.' Lettre a Eevnond (1714) 

 (E. 702 b ; G. iii. 607). 



