200 JMWAtfCEMfcNT OF LEARJfTKO. [BOOK V. 



the thorough examination of a science, he should have some 

 useful rules of discovery ; but after he hath made a con 

 siderable progress in the science itself, he may, and ought, to 

 find out new rules of invention, the better to lead him still 

 farther. The way here is like walking on a flat, where, after 

 we have gone some length, we not only approach nearer the 

 end of our journey, but also have a clearer view of what 

 remains to be gone of it ; so in the sciences, every step of the 

 way, as it leaves some things behind, also gives us a nearer 

 prospect of those that remain : and as we report this parti 

 cular topical invention deficient, we think proper to give an 

 example of it in the subject of gravity and levity. 



1. Let inquiries be made what kind of bodies are suscep 

 tible of the motion of gravity ; what of levity ; and if there 

 be any of a middle or neutral nature. 



2. After the simple inquiry of gravity and levity, proceed 

 to a comparative inquiry; viz., which heavy bodies weigh 

 more, and which less, in the same dimensions ; and of like 

 ones, which mount upwards the swifter, and *yhich the 

 slower. 



3. Inquire what effect the quantity of the body has in the 

 motion of gravity. This at first sight may appear a needless 

 inquiry, because motion may seem proportionable to quantity ; 

 but the case is otherwise. For although in scales quantity is 

 equal to the gravity, yet where there is a small resistance, as 

 in the falling of bodies through the air, quantity has but 

 little force to quicken the descent ; but twenty pounds of 

 lead, and a single pound, fall nearly in the same time. 



4. Inquire whether the quantity of a body may be so in 

 creased as that the motion of gravity shall be entirely lost, 

 as in the globe of the earth, which hangs pendulous without 

 falling. Quaere, therefore, whether other masses may be so 

 b rge as to sustain themselves 1 For that bodies should move 

 to the centre of the earth is a fiction ; and every mass ol 

 ma tter has an aversion to local motion, till this be overcome 

 by some stronger impulse. 



5. Inquire into the effects and nature of resisting mediums, 

 aa to their influencing the motion of gravity ; for a falling 

 body either penetrates and cuts through the body it meeta 

 in its way, or else is stopped by it. If it pass through, there 

 is a penetration, either with a small resistance, as in air, 01 



