A Treatife cf B O D I E S. Chap. 8. 



with a great velocity, is as powerful"! in effect when it gireth a 

 blow, as a harder thing going (lowly. And accordingly expe- 

 rience teacheth us, that a tallow candle (hot in a gun will go 

 throrgha board or kill a man. Wherefore light having fuch 

 an infinite celerity, fhould allb have an unrefutable force, to 

 pierce and fhatter, not onely the aire, but even the hardeft bo- 

 dies that are. Peradventure fome may think it reafonable to 

 grant the confluence ( in due circurnftances ) fince experience 

 teacheth us , that the congregation of a little light by a 

 glafle, will fet very folid bodies on fire, and will melt metals 

 in a very fhort fpace ; which fheweth a great activity : and the 

 great a&ivity fheweth a great percufliom burning being effe<5t- 

 ed by a kind of attrition of the thing burned. And the great 

 force which fire fheweth in gunnes, and in mines, being but a 

 multiplication of the fame, doth evidently convince that of its 

 own nature it maketh a ftrong percuflion, when all cfue cir- 

 curnftances concurre. Whereas it hath but little erTcft. if the 

 due circurnftances be wanting; as wetnayobferve in the infen- 

 . fible burning of fo rarified a body as pure fpirit of wine converv 

 ted into flame. 



But we muft examine the matter more particularly,and muft 

 feek the caufe why a violent effect doth not alwaycs appear, 

 wherefcever light ftriketh ; for the which we are to note 

 that three things do concurre to make a percu/TJon great: The 

 bigneflfe, the denfity, and the celerity of the body moved. Of 

 which three there is onely one in light ; to wit, celerity: for it 

 hath the greateft rarity, and the rayes of it are the fmallcft par- 

 cels of all naturall bodies. And therefore fince oaely celerity is 

 confiderable in the account of lights percuflions, we muft exa- 

 mine what celerity is neceflary to make the ftroke of a ray feofi- 

 ble-- firft then we fee that all the motes of the aire, nay even fea- 

 thers and ftraws, do make no fenfible percuflfion when they fall 

 upon us: therefore we muft in light have at the leaft a celerity 

 that may be to the celerity of the ftaw falling upon our hand 

 ( for example ,) as the denfity of the ftraw is to the denfity of 

 light, that the percuffion of light may be in the leaft degree fen- 

 /iblc. But let us take a corn of gunpowder in ftead of a ftraw 

 (between which there cannot be much difference) and then 

 putting that the denfity of fire is to the denfity ofgunpowder as 



