AND THE THEORY OF LIGHT. 63 



from slow rays, nor red rays from blue rays, nor constitute 

 fits of easy transmission and easy reflection. But this is 

 not the place to discuss this subject. 



94. The experiments hitherto described led to no arith- 

 metical law, I entertained strong hopes, however, that 

 the difliculty would not be great ; but when I first began 

 to experiment in the way described I had no idea that 

 the incident light, or pitch of the ether, was so incon- 

 stant, so continually changing as I have found it to be, I 

 soon became convinced that nature in this as in other in- 

 stances never repeats herself, and that every moment of 

 time, could we trace time backwards, could thereby be 

 distinguished from another. I have every reason, how- 

 ever, to think, that by means of motion we shall soon be 

 able to invent some photometer which shall be available 

 for scientific purposes, 



95, After having made an immense number of experi- 

 ments it was found necessary, for the sake of reference, to 

 arrange them under two heads, distinguished by the nature 

 of the motion, viz. 1st, Horizontal; 2ndly, Perpendicular 

 motion. 



In horizontal motion the figure, or disc, moves parallel 

 to the machine ; in perpendicular motion the figure moves 

 perpendicular to the machine, or parallel to the axis. 

 The phenomena caused by horizontal motion may be 

 divided into three classes : 



I. Class. When light is reflected from the figure, or 



disc, representing coloured reflection. 



II. Class. When light is transmitted through holes 



in the disc, representing transparent coloured 

 media. 



III. Class. Coloured shadows, or penumbrse, showing 

 how refraction produces colour. I call these 

 Solar Spectra by reflection. 



