CONJECTURES RESPECTING THE PRINCIPLES 

 OF THE HARMONY OF COLOURS. 



SINCE the foregoing paper was written, I have at 

 different times repeated most of the experiments 

 therein described, and have made a variety of others, 

 with a view to the farther investigation of this curious 

 subject ; and from the results of these inquiries I have 

 been enabled to form some conclusions and conjectures 

 which may perhaps be thought not altogether uninter- 

 esting. 



Whenever a beam of coloured light of any species, 

 and a beam of white or colourless light of equal in- 

 tensity, arriving in different directions and at equal 

 angles of incidence at a plane white surface, illuminate 

 that surface together, if a solid opaque body of any 

 kind be placed in each of these beams of light, just 

 before the illuminated plane, in such a manner that 

 the two shadows cast on the plane by these opaque 

 bodies may be near each other, the intensities of these 

 shadows will be equal, and they will both appear to be 

 coloured, but of very different hues. That which is 

 illuminated by the coloured light will be of the colour 

 of that light, — which is what would naturally be ex- 

 pected to happen by a person who had never seen the 

 experiment, — but that which is illuminated by the 

 colourless light, and by that alone, instead of appearing 



VOL. IV. 5 



