96 ESSAYS anp OBSERVATIONS 
QueER. XXIV. How does light preferve 
its reCtilinear courfe in pafling through 
air, ether, and other elaftic fluids? Will 
not the difficulty ftill continue, whatever 
fabtility or rarity is afcribed to thefe me- 
diums ; fince the powers from whence their 
elafticity arifes, muft prevail through all . 
the three fpaces that interveen their 
particles ? Mutt we not, therefore, fuppofe, 
that the rays of light are not fubje€ to 
thefe repulfive powers, though they pafs 
through the fphere of their action? Does 
not the refraction of light towards the 
perpendicular, out of the celeftial fpaces 
nto air, even prove that it is attracted by 
the particles of air; Would it not be ex- 
travagant and incongruous beyond mea- 
fure, to imagine the ether fo fubtile, in 
refpect of light, that, though it be driven’ 
out of the way by the rays, as air is by 
commo!r 
of air or their dihance from one arother, by whieh their 
repulfive powers are probably terminated (Newt. Princip.) 
e ‘ 
Why is found, therefore, refleGed fo regularly from’, 
fuch bodies, that the echo is faintly hear, except at am 
ange of incidence equal to the angle of reflexion? 
