476 



JAMES CLERK MAXWELL. 



Cavendish Laboratory. The description is taken from Max- 

 well's paper in the Phil. Trans, for 1860. 





Fig. 2. 



Fig. 2 represents the instrument. At A B is placed the 

 apparatus represented in Fig. 3, in which A' B' represents a 

 rectangular frame of brass, having a rectangular aperture of 



6x1 inches. On this frame are placed six brass sliders, 

 X Y Z. Each of these carries a knife-edge of brass in the 

 plane of the surface of the frame. 



At E (Fig. 2) is a fine vertical slit. At e, M' and M 

 are three plane mirrors, each inclined at 45 to the sides of 

 the box. P P 7 are two prisms (angles 45), and S is a 

 concave silvered glass of radius, 34 inches. 



If light enter the box at E, it will be reflected at e, and 

 a portion of the pencil, after passing through the prisms, will 

 be reflected from S, and after again traversing the prisms 

 will form a spectrum at A B. 



The six movable knife edges above referred to form 

 three slits, X Y Z, which may be so adjusted as to coincide 



