lie 
MR. J. G. LRATHEM ON THE THEORY OF THE 
Polar Reflection from Cobalt. Green Light. 
Angle of 
incidence. 
Calculated value of 
^,,-x + 180°. 
Zeeman’s observed 
value of 
VI - 180°. 
dp -b m — X — 360°. 
50° 
270° 23' 
25° 9' 
-64° 28' 
(10° 
265° 34' 
32° 30' 
-61° 56' 
72° 
256° 13' 
45° 51' 
-57° 56' 
This shews fairly good agreement if x is about 61° 30b In the above d is calcu¬ 
lated from the constants for yellow light. 
Equatorial Reflection from Cobalt. White Light. 
Angle of 
incidence. 
Calculated value of 
A - -b 180°. 
Drude’s observed 
value of 
m — 180°. 
d m — X — 360°. 
35° 
337° 39' 
-77° 24' 
-99° 45' 
60° 
328° 40' 
-25° 27' 
-56° 47' 
75° 
315° 59' 
-12° 56' 
-56° 57' 
83° 
302° 9' 
-12° 57' 
-70° 48' 
Here the agreement is not so good ; the last three angles of incidence would 
indicate that x is about 61° 30'. Drude’s method is that of minimum rotations, 
wherein errors of observation influence the phase to a much greater extent than in the 
method of null-rotations. 
The following experiments are from a paper of Zeeman’s (‘ Communications from 
the Leiden Laboratory of Physics,’ No. 5):— 
Polar Reflection from Cobalt. White Light, = 430 C.G.S. 
Angle of 
Calculated value of 
Zeeman’s observed 
value of 
10-’ X /(. 
/Calculated value of 
incidence. 
log'io (/'/') - login L'- 
\ Observed value of/< / 
45° 
1-2333 
1-58 
108-3 
60° 
1-2092 
1-50 
107-9 
73° 
1-1413 
1-17 
118-3 
wherein L' = 2cX (— C^) yo/RL 
