40 NATURAL HISTORY. 



Friar Bacon walked between two steeples : which was 

 thought to be done by glasses, wl^n he walked upon 

 the ground. 



Experiments in consort touching impulsion and per 

 cussion. 



763. A weighty body put into motion is more easily 

 impelled, than at first when it resteth. 1 The cause is 

 partly because motion doth discuss the torpor of solid 

 bodies ; which, beside their motion of gravity, have in 

 them a natural appetite not to move at all ; and partly 

 because a body that resteth doth get, by the resistance 

 of the body upon which it resteth, a stronger compres 

 sion of parts than it hath of itself: and therefore need- 

 eth more force to be put in motion. For if a weighty 

 body be pensile, and hang but by a thread, the per 

 cussion will make an impulsion very near as easily as 

 if it were already in motion. 



764. A body over-great or over-small, will not be 

 thrown so far as a body of a middle size : 2 so that (it 

 seemeth) there must be a commensuration or propor 

 tion between the body moved and the force, to make 

 it move well. The cause is, because to the impulsion 

 there is requisite the force of the body that moveth, 

 and the resistance of the body that is moved : and if 

 the body be too great, it yieldeth too little ; and if 

 it be too small, it resisteth too little. 



765. It is common experience, that no weight will 

 press or cut so strong, being laid upon a body, as fall 

 ing or strucken from above. It may be the air hath 

 some part in furthering the percussion ; but the chief 

 cause I take to be, for that the parts of the body 



l Arist, Mech. Qusest. 32. 2 Id. ib. 35. 



