154 PROCTOR, ON LIGHT. 
ber, with air intervening, we have a considerable amount of 
light reflected ; the light which penetrates the series becomes 
rapidly less; from the effects of reflection and absorption, 
it becomes at a given depth quite inappreciable. We replace 
the films of air by water; less light is reflected, as has been 
explained, the light is transmitted more freely, consequently 
it descends to a greater depth before it becomes inappreci- 
able. If the water is replaced by Canada balsam, the re- 
flection is again diminished, while the transmission is facili- 
tated; and this takes place even though the balsam absorbs 
more light than the water, and the water more than air; 
but it is self-evident that if the reflecting power had con- 
tinued the same, while the absorbing power had increased, 
there would have been a diminution both in the reflected and 
transmitted light. From these considerations we may state 
as arule that, of bodies with plane surfaces, the reflecting 
power is greatest when the density is greatest, the laminz 
thinnest, the intervening medium lightest, and the absorbing 
power of the two least. The reflecting power is least when 
the density is least, the substance homogeneous (free from 
lamination, &c.), and the absorbing power greatest. We have 
thus come to a conclusion regarding the first essential of a 
white or a black surface, viz., the circumstances regulating 
the amount of light reflected. A second essential is that all 
colours shall be reflected equally ; for if one colour is re- 
flected more than another, instead of having gradation from 
black to white, we have shades of the reflected colour. We 
will suppose, therefore, that our surface reflects all colours that 
fall upon it with equal facility, and now pass on to the third 
element. If the surface is a perfect plane, light falling on it 
is reflected at an angle equal to the angle of incidence, with- 
out suffering other changes in the character of the beam ; 
consequently when the eye is directed to a given point on the 
surface, a line drawn from the surface at an equal angle on 
the other side of the perpendicular will point to the source of 
that light which enters the eye. If that source emits blue, 
red, or yellow light, blue, red, or yellow light will enter the 
eye, and the surface reflecting it will appear to have such a 
colour. How, then, can any smooth surface appear white 
when surrounded by objects of all colours? The fact is, no 
flat, smooth surface appears white when surrounded by ob- 
jects of various colours. 
If you have a surface of polished silver, it reflects and ap- 
pears of the colour of the objects from which the reflected 
light emanates. If the silver, instead of being polished, is 
dead white, it apparently ceases to reflect the colours of the 
