86 ESSAYS AND OBSERVATIONS 



water and other tranfparent liquors, this 

 muil certainly be the cafe, if their globular 

 particles touch one another, as is commonly 

 concluded from their incompreffibility : for, 

 as a number of fpheres laid together leave no 

 redilinear paffages between them, the tranf- 

 mitted light muft pafs thro' the component 

 particles j and therefore the pores, by which 

 it enters, muft be much lefs than the whole 

 hemifpherical furfaces of the particles which 

 evidently conftitute the inequalities of the ge- 

 Deral furface of the liquor *. 



QuER. XXIV. How does light preferve 

 ks reftilinear courfe in paffing thro' air, atber 

 and other elaftic fluids ? Will not the diffi- 

 culty ftill continue, whatever fubtility or ra- 

 rity is afcribed to thefe mediums j fince the 

 powers from whence their elafticity arifes^ 

 muft prevail thro' all the free fpaces that in- 

 terveen their particles ? Muft we not, there- 

 fore, fuppofe, that the rays of light are not 



fubjeit 



* We are certain, that the inequalities of a craggy rock 

 «r roagh wall are much greater than the particles of air 

 <ir tbeir diftance from one another, by which their le- 

 pulfive powers are probably terminated (Neivi. Princip.): 

 Why is found, therefore, reflected fo regularly from fuch 

 podies, that the echo is faintly heard, except at an angle of 

 i|ipdence equal to the angle of reflexion ? 



