LIGHT. 
of a ray between the edges of two very tliin 
planes, at ditfercnt apertures ; which is at- 
tended with this peculiar circumstance, that 
the attraction of one edge is increased as 
the other is brought nearer it. 
The rays of light, in their passage out of 
glass into a vacuum, are not only inflected 
towards the glass, but if they fail too ob- 
liquely, they will revert back again to the 
glass, and be totally reflected. Now the 
cause pf this reflection cannot be attributed 
to any resistance of tl:e vacuum, but must 
be entirely owing to some force or power 
in the glass,, which attracts or draws back 
the rays as they were passing into the va- 
cuum. And this appears further from hence, 
that if you wet the back surface of tlie glass 
with water, oil, honey, or a solution of 
quicksilver, then the rays which would 
otherwise have been reflected, will pervade 
and pass through that liquor ; which shows 
that the rays are not reflected till they 
come to that back surface of the glass, nor 
even till they begin to go out of it ; for it at 
their going out they fall into any of the 
aforesaid mediums, they will not then be 
reflected, but will persist in their former 
course, the attraction of tlie glass being in 
this case counterbalanced by that ot the 
liquor. 
M. Maraldi prosecuted expeiimfents simi- 
lar to those of Sir I. Newton, on inflected 
light. And his observations chiefly respect 
the inflection of light towards other bodies, 
by which their shadows are partially illumi- 
nated. Acad. Paris 1723, Mem. p. 159. 
See also Priestley’s Hist. p. 521, &c* 
From the mutual attraction between the 
particles of light and other bodies, arise two 
other grand phenomena, besides the inflec- 
tion of light, which are called the reflection 
and refraction of light. It is well known 
that the determination of bodies in motion, 
especially elastic ones, is changed by the 
interposition of other bodies in their way ; 
thus also light, impinging on the surfaces of 
bodies, should be turned out ot its course, 
and beaten back or reflected, so as, like 
other striking bodies, to make the angle of 
its reflection equal to the angle of inci- 
dence. This, it is found by experience, light 
does ; and yet the cause of the effect is dif- 
ferent from that just now assigned, for the 
rays of light are not reflected by striking 
on the very parts of the reflecting bodies, 
but by some power equally diffused over 
the whole surface of the body, by which it 
acts on the light, either attracting or re- 
pelling it, without contact : by which 
same power, in other circumstances, the 
rays are refracted ; and by wliich also the 
rays are first emitted from the luminous 
body ; as Newton abundantly proves by a 
great variety of arguments. See Heflec- 
TioN and Refraction. 
That great author put it past doubt, that 
all those rays which are reflected do not 
really touch the body, though they approach 
it infinitely near; and that those which 
strike on the parts of solid bodies adhere to 
them, and are, as it were, extinguished and 
lost. Since the reflection of the rays is as- 
cribed to the action of the whole surface of 
the body without contact : if it be asked 
how it happens that all the rays are not 
reflected from every surface, but that, while 
some are reflected, others pass through and 
are refracted ? the answer given by New- 
ton is as follows : Every ray of light, in its 
passage through any refracting surface, is 
put into a certain transient constitution or 
state, which in the progress of the ray re- 
turns at equal intervals, and disposes the ray 
at every return to be easily tiansmitted 
through the next refracting surface, and be- 
tween the returns to be easily reflected by it : 
which alteration of reflection and transmis- 
sion, it appears, is propagated from every sur- 
face,aud to all distances. Whatkind ofaction 
or disposition tlris is, and whether it consists 
in a circulating or vibrating motion of the 
ray, or the medium, or something else, he 
does not inquire ; but allows those who are 
fond of hypothesis to suppose that the rays 
of light, by impinging on any reflecting or 
refracting surface, excite vibrations in the 
reflecting or refracting medium, and by that 
means agitate the solid parts of the body. 
These vibrations, thus produced in the 
medium, move faster than the rays, so as to 
overtake them ; and when any ray is in that 
part of the vibrajion which conspires with 
its motion, its velocity is increased, and so 
it easily breaks through a refracting surface ; 
but when it is in a contrary part of the vi- 
bration, which impedes its motion, it is 
easily reflected; and thus eveiy ray is suc- 
cessively disposed to be easily reflected or 
transntitted by every vibration which meets 
it. These returns in the disposition of any 
ray to be reflected, he calls fits of easy 
reflection; and the returns in the disposi- 
tion to he transn/itted, he calls fits of easy 
transmission; also the space between the 
returns, the interval of the fits. Hence 
then the reason why the surfaces of all thick 
transparent bodies reflect part of the light 
incident upon them, and refract the rest 
