164 PROCTOR, ON LIGHT. 
amount of the same kind of matter, only wanting the air, 
transmits light freely and reflects but little. 
A waxy lustre has the reflection from the primary surface 
supplemented by reflections from irregular particles beneath 
the surface; we have the phenomena also illustrated, and 
that on a larger scale, in polished marble and glazed earthen- 
ware, while the earthenware without a glazing reflects light 
without the appearance of lustre to the naked eye. I would 
willingly have enlarged upon the subject of lustre and its 
theories, but time is outstripping me, and I must hasten on. 
The colour reflected from a substance is not always the 
same, and not always different from that transmitted. It is 
often, evidently, only with a conventional correctness that we 
state the colour of a material. We say gold-leaf is yellow, 
but we might also say that it is green—the transmitted light 
being different in this case from the reflected. But, further 
than this, we may say that gold is yellow by reflected light ; 
but only as a convenient and conventional statement is it 
admissible, for we have seen that gold is brown, yellow, red, 
purple, and blue. It might be difficult to prove that these 
colours were any of them purely reflected. We have just 
seen reason to believe that reflection is always accompanied 
by transmission through a certain depth—that is, ‘ through 
that thickness of matter concerned in ordinary reflection ;” 
and we have just speculated upon the probability of trans- 
mission being always accompanied with some degree of re- 
flection. I might instance a long list of colouring principles, 
each of which reflects a colour different from that which it 
transmits, but I will only draw your attention to my specimens 
of the familiar mauve and magenta, which reflect respec- 
tively green and yellow light. I cannot, however, leave the 
subject of reflection without questioning the correctness 
of another common statement. When light falls upon glass 
and is reflected, we say the glass reflects it; overlooking, it 
often happens, that the rare medium is, equally with the 
denser, concerned in the reflection which takes place. From 
a bright surface of glass in air there is considerable reflec- 
tion; from the same surface when under water there is com- 
paratively little, and if immersed in- turpentine there is 
almost none. Is it not the surface of air, water, and tur- 
pentine, in contact with the glass, in these several instances, 
which reflected the light? Ifso, we may say that air reflects 
most light, water less, and turpentine least. If it is the glass 
which reflects in all three cases—the glass reflects most light, 
the glass reflects less light, and the glass reflects least light. 
Do not suppose that I wish to persuade you that the glass 
