248 THE WORLD MACHINE 



ing in all things to the common rules of mechanical motions. 

 This depends upon three suppositions : 



" First, that all celestial bodies whatsoever have an attrac- 

 tion or gravitating power towards their own centres, whereby 

 they attract not only their own parts and keep them from fly- 

 ing from them, as we may observe the Earth to do, but that 

 they also do attract all the other celestial bodies that are within 

 the sphere of their activity ; and consequently, that not only 

 the Sun and Moon have an influence upon the body and motion 

 of the Earth, and the Earth upon them, but that Mercury, Mars, 

 Jupiter and Saturn also, by their attractive powers, have a 

 considerable influence upon its motion, as in the same manner 

 the corresponding attractive power of the Earth hath a con- 

 siderable influence upon every one of their motions also. 



" The second supposition is this, that all bodies whatsoever 

 that are put into direct and simple motion will so continue to 

 move forward in a straight line till they are, by some other 

 effectual powers, deflected and sent into a motion describing a 

 circle, Ellipsis, or some other more compounded curve line. 



" The third supposition is, that these attractive powers are 

 so much the more powerful in operating by how much the nearer 

 the body wrought upon is to their own centres. Now what these 

 several degrees are I have not yet experimentally verified ; but 

 it is a notion which, if fully prosecuted as it ought to be, will 

 mightily assist astronomers to reduce all the celestial motions 

 to a certain rule, which I doubt will never be done without it. 

 He that understands the nature of the circular pendulum and 

 of circular motion will easily understand the whole of this prin- 

 ciple, and will know where to find directions in nature for the 

 true stating thereof. 



" This I only hint at present to such as have ability and 

 opportunity for prosecuting this inquiry, and are not wanting 

 of industry for observing and calculating, wishing heartily such 

 may be found, having myself many other things in hand which 

 I would first complete, and therefore cannot so well attend it. 

 But this I durst promise the undertaker, that he will find all 

 the great motions of the world to be influenced by this principle, 

 and that the true understanding thereof will be the true per- 

 fection of astronomy." 



You perceive how closely they are pressing the quarry. 



