of the Plane of Polarization of Light. 313 



Iron mirror No. 3. 



o / 



Glass and platinum +1 42 



Glass, platinum and iron -f 3 48 



Rotation due to iron ..:.... + 26 



Iron mirror No. 4: — 



After this mirror had been covered with a tolerably trans- 

 parent layer of iron, half of it was covered with a farther 

 deposit of iron ; so that this half was dark brown, though 

 transparent. The platinum and iron were then removed from 

 one portion of the glass. t 



Rotation by glass alone +2 12 



„ glass, platinum, and thin iron film + 3 42 



v glass, platinum, and thick iron film + 5 54 



Rotation produced by thin iron film . . + 1 30 

 „ „ thick „ . . +3 42 



As already remarked, the rotation produced by the film of 

 platinum is not measurable. 



Cobalt. 

 Cobalt mirror No. 1. 



o / 



Rotation by glass and platinum . . . . +1 18 

 „ glass, platinum, and cobalt . + 2 36 



Rotation by cobalt +118 



Cobalt mirror No. 2, Very transparent. 



Rotation by glass and platinum . . . . + 1 30 

 „ glass, platinum, and cobalt . +2 34 



Rotation by cobalt +14 



Cobalt mirror No. 3. A portion of the same piece as 



No. 2. 



o / 



Rotation by glass and platinum . . . . + 1 30 

 „ glass, platinum, and cobalt . + 2 30 



Rotation by cobalt +10 



The two mirrors placed one behind the other still trans- 

 mitted sufficient light. The rotation produced by the two 

 cobalt layers together was found to be the sum of those 

 produced by the two separately, viz.: — 



o / 



Rotation due to 2 and 3 together ... +25 

 Phil. Mag. S. 5. Vol. 18. No. 113. Oct. 1884. Y 



