1835.] Accidental and Complementary Colours. 25 



the plane mirror to perform its part. If dark greens or 

 blues be employed the experiment will not succeed, but 

 with darkish reds and yellows no obstruction is offered. 



17. For a complete instrument* the following glasses 

 may be chosen : — 



1. Red. 



2. Orange. 



3. Yellow. 



4. Light green. 



5. Light blue. 



6. Light indigo. 



7. Light violet. 



8. Light milky- white. 



9. A faint shade of black. 



The two latter may, however, be omitted, as the results 

 obtained by their means are not altogether satisfactory. 



18. The form of the instrument may, however, be much 

 varied. An oblong plane mirror with several smaller 

 oblong pieces of stained glass, the lengths of which must be 

 placed at right angles to the length of the plane mirror. 

 Thus, as many accidental colours will be observed as there 

 are primitives. 



19. I find that the coloured solutions (11) placed on a 

 plane mirror will afford all the results contained in my first 

 and those in the former part of this paper. A box may 

 be formed with a plane mirror at the bottom, well luted 

 round the edge to prevent the solutions from spoiling the 

 silvering ; but the best mode of exhibition is to fix the 

 mirror at the bottom of a cylindrical glass with a perfectly 

 flat surface, the mirror being placed on the outride, or the 

 outside bottom itself may easily be silvered. 



20. In offering these experiments to the notice of your 

 readers, I may be allowed to state that they are altogether 

 opposed to the existing theory of accidental colours. At 

 the same time, I do not feel myself suflftciently prepared to 

 offer another theory that may chance to be received as 

 satisfactory.*!* 



21 . Not having the advantage of reference to a scientific 



* An ingenious friend has suggested the term " Perichromascope," or " Pros- 

 chromascope," as applicable to this little instrument. 



t I am aware that M. Plateau has a new theory of accidental colours, but I 

 have not been so fortunate as to see it. 



