PHYSICAL ann LITERARY. 43 
know, further, that very thin bodies, (as 
foap-bubbles, Mufcovy-glafs, and air in 
a fracture of glafs or ice, or between two 
lenfes), while they reflect fome rays of all 
colours from the firft furface, reflect only 
particular colours at the fecond*? Do 
not thefe facts lead us naturally to fup- 
pofe the firft fort of light to be only a part 
of the incident light refleéted from the 
firft furface of the body ; and the fecond, 
a part of what had paffed on, reflected 
from the pofterior furfaces of the fuperfi- 
cial particles? 
AG Oy toa) & 
Concerning the Caufe of the different Refran- 
gibility of the Rays of Light +. 
_ 36. IN order to account for the differ- 
ent refrangibility of the differently-colour- 
* Newt. Opt, book 2. part 3, prop. 12. 
Ke | 5B Although the doétrine contained in this feftion has 
t “been already publifhed in the Philofophical tranfa@ions 
for 1753, (vid: vol, xlviii, part 1. p. 262, &c.), having 
: been 
