O. N. Rood on Dove's Theory of Lustre. 343 
and the white paper alone is perceived. This disagreement is 
not a cause of astonishment when we reflect that de Haldat’s 
original experiment waited nearly half a century for confirma- 
tion. 
To Brewster’s own theory, the simple objection, which has 
already been made by others, that we daily perceive lustre 
plainly with one eye, would seem sufficient. 
Propuction or Lusrre 1n Monocutar Vision, 
I proceed now to describe some experiments where by the 
action upon asingle eye.of two masses of light of unequal inten- 
sity, the idea of lustre is produced. 
1. If a dise of colored card-board, out of which a number of 
sectors has been removed, be made to rotate rapidly, and an 
object be viewed through it by a single eye, two masses of light 
will reach the eye, which apparently proceed from the object; 
one is reflected from the surface of the disc, the other emanates 
from the object behind the disc, and passes through the first 
mass of light. Dark objects viewed in this way assume to me to 
asmall extent an appearance like that of blackened glass. The 
effect is not at all striking, and would be overlooked by many 
persons; I therefore prepared paper in a peculiar way so as to 
unitate distantly the appearance of foliated graphite or crumpled 
mica. 
White smooth drawing paper was rubbed over irregularly 
with a brush slightly moistened with a weak wash of India ink or 
lampblack; when dry another wash of a deeper hue applied as 
before, care being taken to leave many small spots untouched. 
The final wash was laid on with pure black. If the brush be 
kept nearly dry and passed only lightly over the paper, it is easy 
to obtain a surface bearing some very distant resemblance to the 
minerals above mentioned; it is of course without lustre. Sim- 
ilar papers were prepared with red and blue water colors. : 
When these papers were held behind discs of ultramarine 
or orange-tinted paper, from which equal alternate sectors had 
been removed, and which were revolving at such rates that their 
surfaces seemed uniform,.or at lower rates, they often-appeared 
to a single eye, highly lustrous, This was true of the preparec 
Paper in a state of rest; when moved slightly by the hand it 
glittered strongly. Dark photographs of tin foil held behind a 
revolving disc of ultramarine paper and viewed by a single eye, 
assume often to a striking degree the lustre and appearance of 
foliated graphite. : 
2. If a piece of this peculiarly blackened paper $ of an inch 
Square be placed in a blue field, (rather light ultramarine paper,) 
and be steadily regarded for some minutes by one eye it assumes 
& red orange-hue and appears suspended over the blue paper 
Am. Jour. Sc1—Srconp Series, Vor. XXXI, No. 93.—May, 1861. 
