PROCTOR, ON LIGHT. 155 
objects; but the microscope reveals the truth, that now the 
surface is not one smooth plane, but consists of an infinitude 
of curves, each reflecting all the colours of the surrounding 
objects ; but-so minute are these reflections that, to the naked 
eye, they cannot be separably distinguished, and the result 
is an impression of uniform colour; or if the various colours 
fall upon it in due proportion, its appearance is white: this 
is the nature of what takes place upon all white surfaces. 
You will say, How will it apply to such materials as porce- 
lain, which have not a dead-white, but a polished-white, sur- 
face? In reply, I must direct your attention to the fact that 
in glazed porcelain there are two distinct reflections—that 
from the glazing is similar to that from the polished silver, 
but the glazing is transparent, the light passing through it 
falls upon matter which reflects hght im the same condition 
as that which is reflected from the dead-white silver.* 
Now let us return to the subject of ‘‘ body,” and we under- 
stand at once the difference between the white lead and the 
magnesia. They are both transparent in their individual 
particles, but the magnesia more so. They are both bodies 
possessed of considerable refractive power, but the lead more 
so. When air intervenes between their particles, the reflec- 
tive power of both so much exceeds that of air that they are 
highly reflecting and very slightly transmitting; but the less 
absorbing power of the magnesia makes it the whitest—the 
more reflecting of the two. But when oil intervenes, as would 
be the case if they were used for pigments, the refractive 
power of the magnesia so nearly coinciding with that of the 
oil that much transmission and little reflection is the result, 
this constitutes what painters call want of body. But the 
lead so greatly exceeds the oil in refracting power that its 
reflective property is not much interfered with, and even with 
its greater absorbing power it reflects much and transmits 
little light, this being what painters call great body. 
I have here specimens of carbonate of magnesia and white 
lead. You will observe that the magnesia, when dry and seen 
by transmitted light, consists of small particles which are 
transparent when seen singly, but look opaque where they are 
* The manner of its reflection, however, being somewhat analogous to 
that of the bundle of plates, for the porcelain consists of transparent particles 
superposed upon one another, the various particles having different powers 
of transmission, reflection, and refraction, you will at once perceive that 
the same circumstances which changed the amount of one or other property 
in the bundle of plates will do the same in the porcelain. The more nearly 
the various parts have the same refractive power, the more light will be 
transmitted, the less reflected. 
