EXPERIMENTS OIC DOUBLE VISION. 



Homogeneous Homogeneous colours of different shades combine with 



colours com- the greatest facility. Thus a strong red and a faint red give 



a mean tint of red. What appears very astonishing is, that 



Black and black and white comport themselves as pigments of the same 



white unite f l ° 



with and modi- colour would do. White, which is the result of a union of 



fy an colours, all the primary colouring rays, renders colours lighter, as 

 a mechanical mixture of a white powder would the pigments 

 that represent the other colours. Thus red and white give 

 a flesh colour. Black, which is merely the absence or pri- 

 vation of colour, might be supposed to produce no effect on 

 the organ of sight ; yet it has just the same as a mixture of 

 any black powder would with the pigments that produce 

 other colours. Thus light blue or green with black gives 

 the perception of dark blue or green. Glaring colours, 

 such as red and orange, less readily associate with black : 

 but white and black, the white pasteboard being placed on 

 a black ground, and the black pasteboard on a whit* 

 ground, produce the sensation of gray, like a mixture of 

 ivory black and chalk. 



I should tire the reader, if I were to relate all the differ* 

 ences I have observed in colours with respect to the degree 

 of facility with which they combine, or rather associate the 

 effects they produce separately on the two eyes. But I 

 cannot pass over another class of facts, which pertain ta 

 the same theory, and may serve to elucidate it. These facts 

 Double -vision relate to the double vision of objects resembling each other 

 of objects dif- . co i our but differing in form, or differing both in form 



fen <g in figure. ' I 



Parallel igrams and colour at the same time. Little parallelograms of paste- 



dtedtections " boarJ ' either black ' whUe ' or of various homogertcal co- 

 lours, twelve lines long and four broad, placed on the op- 

 posite sides of the vertical plane of the apparatus, one pa- 

 rallel the other perpendicular to the plane, exhibit the 



form a cross, appearance of a cross with equal arms. Two equal disks, 

 eight lines in diameter, placed on opposite sides of the same 

 vertical plane, are so blended together, that it is impossible 

 to distinguish them. -Parallelograms like those just des- 



andtheirco- cribed, or squares of unequal size, if of different colours, 



lours blend exhibit by double vision crosses or concentric squares, the 

 wnere they J ^ ' 



join. place of junction or superposition of which exhibits the 



mixed colour, 



X shall 



