SENSATIONS IN TERMS OF l.rMIVOSlTY. 



After passing through the collimator C, the rays emerged as parallel rays ; part passed 

 through the prisms P! and P,, were collected by a lens, L 3 , and a spectrum was formed 

 on a slide, D (which will be more fully described), in which slits could be placed, and 

 an image of the surface of the first prism was formed on the white-red surface of a cube, 

 E, by means of the lens L 4 , so arranged that the image of one edge of the prism fell 

 at a, the other edge falling outside d. The other beam which passed through the 

 collimator was reflected from the surface of the first prism to a mirror, G 1 , and passed 



Fig. 2. 



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3 *\6" 7r^ / 



I > /'/ 



i / 

 z /' 



M, M* / 

 tl^** ' / ." 



<> 

 ,nr 



// 



/ ' 



through a lens, L 8 , then through a bundle of glass, G", placed at an angle to the 

 beam, and on to the surface dc of the cube, a rod, Kj, being placed in its path, to 

 secure that this white beam did not fall on ad, on which the colour mixture fell. The 

 jwrtion of the beam which was reflected from G" was again reflected by G 111 , a silvered 

 mirror, on to etc, a rod, K 2> being placed in its path to prevent it falling on ad. In all 

 three beams, sectors, M 1 , M", and M" 1 , were placed, to allow any or all to be reduced 

 in intensity at pleasure. In the beams X and Y any absorbing medium desired could 



