reflected. 
340. O. N. Rood on Dove's Theory of Lustre, 
Upon substituting dark grey paper for the tin-foil the same 
effects in degree were not produced, owing as it seemed to me, 
to the fact that the well known texture and appearance of the 
paper forcing itself on the attention, precluded the idea of any- 
thing metallic. To remove this difficulty I employed two means. 
1. A crumpled sheet of tin-foil was photographed, and fro 
the negative, prints were taken, by the “‘ammonia-nitrate pro- 
cess,” which were toned to the so-called black of the photograph- 
ers. This furnished dark paper upon whose surface was an 
accurate drawing of the irregularities characteristic of metallic 
be the surface of the paper was of course wholly without 
ustre. 
(2) Upon combining, in black or white fields, a square inch of 
one of those photographs, with the above-mentioned yellow 
paper, and dortas the photograph a little, a representation of 
gold was obtained but little inferior to that given by the use of 
the real tin-foil. 
(6) This photographic paper in combination with orange paper 
(1st circle, orange), made an imitation of metallic copper. 
The ultramarine paper in combination with the photograph 
of tin-foil gave a striking imitation of foliated graphite. The 
blue color is perceived much less than would be expected 
. The surface of a plate of brass 1 inch square was polished, 
and then rather heavily scratched by a coarse file. Into the 
scratches a small amount of yellow or white oil paint was 
rubbed, and upon this prepared surface dark grey or black paper 
was laid and the whole submitted to the action of a press as in 
- copper-plate printing. By this means a drawing of a scratched 
metallic surface was transferred to paper. These markings serve 
also to enable the observer much more easily to direct his atten- 
tion simultaneously to the two impressions presented. 
(2) Upon combining dark grey paper (black and white scale, 
Nos. 18, 19, 20,) prepared in this way with the above-mentioned 
yellow paper, the appearance of a polished, scratched plate of 
gold was obtained, 
(®) When these dark prepared papers were combined with 
yellow paper colored by gamboge (yellow and black scale, No. 9), 
the appearance and lustre of brass was obtained. 
According to Dove’s theory the darker surface in the stereo- 
scope represents the dispersed light, the brighter, that regularly 
the polish of a metallic surface is proportional to 
the smallness in amount of the light it disperses, we should be 
led to expect that by varying the shade of the black paper, we 
should be able to alter the apparent degree of polish of these 
imitated metallic surfaces, 
This is the case: yellow paper, (Ist circle, oran yellow No. 
4,) in combination with b (No. 21,) gives the idea of a very 
———S a 
