48 Mr. W. Baily on Starch and Unannealed 



in fig. 5 by the thick continuous line having dots on one side 

 of it. 



The figure may be drawn in a similar manner to that de- 

 scribed for figs. 3 and 4. 



The locus of plane-polarized light may be investigated 

 without reference to the condition of the rest of the light, by 

 drawing M(0) by equation (13), and marking the direction 

 of polarization at successive points on it by equation (15). 



In figs. 6, 7, and 8 the points through which short straight 

 lines are drawn are points at which the light is plane-polarized ; 

 and the short straight lines through them show the direction 

 of polarization at the points. The dotted lines connecting 

 these points are loci of plane-polarized light. The centres 

 about which small circles are drawn are points at which the 

 light is circularly polarized: and in fig. 6 the dotted lines 

 connecting these circles are loci of circularly polarized light. 

 The signs within the circles indicate the direction of rotation 

 of the aether ; see (21). 



In fig. 6,/> = 45°; in fig. 7, ^ = 22° 30'; in fig. 8, /o=0. 



If the light be passed through an analyzing Nicol with its 

 plane of polarization inclined at an angle p f to SS', we can 

 obtain the intensity of the light at any point as follows : — 



The vibration along the major axis is cos /3 cos t, and that 

 along the minor axis is sin /3 sin t ; so that the vibration in 

 the direction of the plane of polarization of the analyzer is 



cos (p f — a) cos /3 cos t — sin (p r —ot) sin /3 sin t. 



Hence, if I is the intensity of the light after passing the 

 analyzer, 



I = cos 2 (// — a) cos 2 /3 + sin 2 (// — a ) sin 2 /3, 



2I = l + cos2(//— a) cos 2/3. 



The appearance of the light after passing an analyzer 

 might be calculated from this equation, but can be inferred 

 more readily by an inspection of the figures, which show its 

 state before passing. 



We notice that two dark spots will be seen on each branch 

 of M(0), one at each extremity of a diameter, at the points 

 where the vibration is perpendicular to the plane of the ana- 

 lyzer. The spots on the successive branches of M(0) will be 

 alternately on a certain diameter and on the diameter perpen- 

 dicular to it. 



When the incident light is circularly polarized, these spots 

 will move round in circles with unaltered appearance and at a 

 uniform rate as the analyzer is turned uniformly. See figs. 

 2 and 6. 



