ADVANCEMENT OF LEARNING 231 



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 particular 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, pro 

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

 weigh more, and which less, in- the same dimensions; and 

 of like ones, which mount upward the swifter, and which 

 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 

 increased as that the motion of gravity shall be -entirely 

 lost, as in the globe of the earth, which hangs pendulous 

 without falling. Query, therefore, whether other masses 

 may be so large as to sustain themselves ? For that bodies 

 should move to the centre of the earth is a fiction; and 

 every mass of matter has an aversion to local motion, till 

 this be overcome by some stronger impulse. 



5. Inquire into the effects and nature of resisting me 

 diums, as to their influencing the motion of gravity; fora 

 falling body either penetrates and cuts through the body 

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

 through, there is a penetration, either with a small resist 

 ance, as in air, or with a greater, as in water. If it be 

 stopped, it is stopped by an unequal resistance, where 



