ON THE ESSENTIAL PROPERTIES OF MATTER. 471 



Another universal property of matter is reciprocal gravitation, of which 

 the force is directly in the joint proportion of the quantities of matter at- 

 tracting each other, and inversely as the square of their distance. In order 

 to prove that the gravitation towards a given substance, for instance, the 

 weight of a body, or its gravitation towards the earth, is precisely in pro- 

 portion to the mass or inertia of the moveable matter of which it consists, 

 Sir Isaac Newton made two equal pendulums, with hollow balls of equal 

 size : in order that the resistance of the air might be the same with respect 

 to both, he placed successively within the balls a variety of different sub- 

 stances, and found that the time of vibration remained always the same ; 

 whence he inferred that the attraction was proportional in all cases to the 

 quantity of matter possessing inertia. For if any of these substances had 

 contained particles capable of receiving and communicating motion, yet 

 without being liable to gravitation, they would have retarded the vibrations 

 of the pendulum, by adding to the quantity of matter to be moved, without 

 increasing the moving force. The law of gravitation, which indicates the 

 ratio of its increase with the diminution of the distance, is principally 

 deduced from astronomical observations and computations : it is the 

 simplest that can be conceived for any influence, that either spreads from a 

 centre, or converges towards a centre ; for it supposes the force acting on 

 the same substance to be always proportional to the angular space that it 

 occupies. 



Newton appears to have considered these laws of gravitation, which he 

 first discovered, rather as derivative than as original properties of matter ; 

 and although it has often been asserted that we gain nothing by referring 

 them to pressure or to impulse, yet it is undoubtedly advancing a step in the 

 explanation of natural phenomena, to lessen the number of general prin- 

 ciples ; and if it were possible to refer either all attraction to a modification 

 of repulsion, or all repulsion to a modification of attraction, we should 

 make an improvement of the same kind as Newton made, when he reduced 

 all the diversified motions of the heavenly bodies to the universal laws of 

 gravitation only. We have, however, at present little prospect of such a sim- 

 plification. 



It has been of late very customary to consider all the phenomena of 

 nature as derived from the motions of the corpuscles of matter, agitated by 

 forces varying according to certain intricate laws, which are supposed to 

 be primary qualities, and for which it is a kind of sacrilege to attempt to 

 assign any ulterior cause. This theory was chiefly introduced by Bosco- 

 vich,* and it has prevailed very widely among algebraical philosophers, who 

 have been in the habit of deducing all their quantities from each other by 

 mathematical relations, making, for example, the force a certain function 

 or power of the distance, and then imagining that its origin is sufficiently 

 explained ; and when a geometrician has translated this language into his 



* De Viribus Vivis, 4to, 1745; De Lumine, 4to, 1748; De Lege Continuitatis, 

 4 to, 1754; De LegeVirium in Natura existentium, 4to, 1755; De Divisibilitate 

 Materise et Principiis Corporum, 4to, 1757 ; Theoria Philosophise Naturalis, 4to, 

 1763, p. 4, Venice. See also Benvenutus, Physicse Generalis Synopsis, 1754. 



