with Dove's Theory of Lustre. 39 



reflected light in combination with internally reflected or 

 dispersed light, whose combined action produces the idea of 

 lustre." 



Thus by combining in the stereoscope two projections of a 

 pyramid, one drawn in black lines on a white ground, the other 

 in white lines on black ground, Dove found that the pyramid 

 appeared lustrous as though made of graphite. [To me it 

 recalls rather the idea of highly polished glass.] He found also 

 that a yellow and blue surface, when combined in the stereoscope 

 and viewed through a plate of violet glass, produced, in the act 

 of combination, the idea of a polished metal. 



Similar to Dove's theory of lustre is that of Prof. Reute*. 



This view of the nature of lustre opens to us the possibility" 

 of reproducing by the stereoscopic combination of suitably 

 coloured surfaces, the individual lustre and appearance of gold, 

 copper, brass, &c. ; it also affords us a means of examining 

 separately the components which may produce the appearances 

 peculiar to each. 



1. I combined in the stereoscope on white or on black grounds, 

 a piece of tinfoil one inch square with a piece of yellow paper 

 of the same size. The value of the tint on the chromatic circles 

 of Chevreul was, 1st circle, orange-yellow, No. 4. When the 

 field containing the tinfoil was somewhat shaded by the hand 

 or otherwise, the surface seen in the stereoscope could not be 

 distinguished from gold-leaf. The union of the images took 

 place as readily and the illusion was as strong with persons un- 

 accustomed to the use of the instrument. 



2. By combining in the same way tinfoil with orange-tinted 

 paper (1st circle, orange), the lustre and appearance of copper is 

 imitated. 



3. Tinfoil in the act of combination with Nos. 14 and 15 of 

 the red and black scale imitate bismuth. 



4. Tinfoil or silver-foil in the act of combination with ultra- 

 marine paper appears scarcely blue, rather black like foliated 

 graphite. 



5. Gold-leaf in combination with paper of a tint nearly that 

 of the green of the 1st circle imitated murexide. 



6. Gold-leaf in combination with ultramarine paper resembled 

 a surface of graphite. 



Upon substituting dark grey paper for the tinfoil 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 : — 



* Das Stereoscop; C. G. Th. Reute, -Leipzig, 1860. 



