AND THE THEORY OF LIGHT. 17 



reacliing from the sun or luminous body to us^ and were 

 there rays of every imaginable colour, — or were a ray of 

 light a constant or uninterrupted succession of molecules 

 thrown from the sun or luminous body, which would be 

 the same in effect as the infinitely fine wire,^ — there would 

 be no need of shadow in a theory of colour, provided there 

 were also a chromatic elective affinity between each terres- 

 trial object and its special ray. But if light is the effect of 

 pulsations repeated at intervals, darkness or shadow must 

 play a most important part in chromatics, as important a 

 part as it does in the natural landscape or in aerial per- 

 spective. 



28. I therefore feel more disposed to speak in the lan- 

 guage of the painter than in that of writers on this 

 subject; for, although the experiments which I have to 

 bring forward demonstrate, as I believe, the vibratory 

 nature of light, I think it will be more intelligible to speak 

 of light and shade, which can be made visible, than of the 

 number of vibrations or form of waves, until these have 

 been demonstrated or exhibited to the sight. 



29. Besides, it is almost impossible to believe that there 

 should be a system of rays of different velocities in the 

 luminous ether, or that some of the molecules of ether 

 should be disposed to be differently affected from others. 

 It is possible, however, to conceive, nay, it is almost im- 

 possible to resist the conviction, that all natural objects 

 are formed on strict geometrical principles ; that some are 

 capable of reflecting more rays and others fewer; that 

 some are more sensitive to light than others, and that the 

 varying degrees of light from different substances produce 

 an equivalent effect on the retina. Intensity is the effect 

 of repeated pulsations on the same physical point. Of 

 course it is possible that different degrees of intensity 

 may produce different lengths of waves on the retina, or 

 within the medium of refraction, and thus cause colour ; 



SER. III. VOL. I. D 



