Accidental and Complementary Colours. 291 



card, or a similar object, the resulting shadow will be com- 

 plementary to the colour of that part of the spectrum 

 whereon the shadow falls; mingled, however, with a small 

 portion of natural light which imparts a grayish hue to the 

 colour of the shadow : but the result is decided and con- 

 clusive. 



The most refrangible colours are best adapted to the 

 reception of the shadow, as the illuminating power is 

 smaller, and the space occupied by the colour larger, so 

 that the contrast between the fundamental and comple- 

 mentary colours is more readily observed. In the less 

 refrangible colours, the illuminating colour being great, 

 and the space occupied comparatively small, the shadows 

 appear very dark, and sometimes too deep for correct 

 observation of their colour. If the spectrum then be too 

 vivid, it, or portions of it, in succession, may be received 

 upon a plane mirror, and so reflected upon the ceiling, or 

 upon a white screen. The colours become less vivid by 

 reflection, and the shadows consequently more appreciable. 



21. Class 2nd. Coloured glass of every shade and depth 

 of shade, provided light can be transmitted through it, 

 may be employed. If a coloured disk be held before a 

 lamp, or any strong source of light, and the coloured light 

 fall upon white paper, a shadow formed by intercepting a 

 portion of the light will be complementary to the colour of 

 the disk. Coloured solutions contained in an oblong glass 

 frame may be employed, and even vapours such as chlorine, 

 iodine, nitrous acid, &c. 



The stains of the glass, must not, however, be too light, 

 because, as shadows are judged of by contrast, the comple- 

 mentary shadow will appear too dark for the observation 

 of its colour : but this may be remedied by employing two 

 or three thicknesses of glass. Interesting results may be 

 obtained by transmitting light through pairs of disks of 

 different colours, — the accidental colour of each being, of 

 course, modified or changed by such means : thus, green 

 glass transmits green light, a shadow falling into it is pink. 

 The same pink shadow may be produced by passing a light 

 through a yellow and blue disk placed the one upon the 

 other; and so on. 



One of my methods of exhibiting coloured shadows to an 



u2 



