lOG 
MR. J. G. LEATHEM ON THE THEORY OF THE 
a) 
75° 
78° 5T 
00 
o 
o 
o 
CO 
o 
0^1 
00 
o 
00 
86° 
86° 30' 
o 
00 
CO 
X 
137° 37' 
119° 57' 
114° 23' 
101° 32 
89° 17' 
o 
* 
o 
00 
82° 33’ 
76° 29' 
And if Kundt’s observation be accurate, the value of x is about 103". 
18. From the j^receding paragraphs it appears that any rmlue of r lying between 
69° 17' and 82° 22' will account very well for the four Kerr experiments (in the 
case of iron), except that the agreement with Kuxdt’s result in the fourth experi¬ 
ment would be imperfect to the extent of four or five degrees. 
19. The Kerr experiments were also tried on mirrors of nickel and of cobalt, but 
the observations made were so indeSnite that they are of little use as a test of the 
present theory. In the case of polar reflection from nickel, when the incident light 
is polarised perpendicularly to the plane of incidence, Kundt found that the rotation 
changes sign for an angle of incidence somewhere between 50° and 60°. I have 
calculated (for yellow light) the values of the vector angle of B cos t’/A for these 
angles of incidence, and find them to be 
rc - 67° 12' for i - 50°, 
a; - 57° 12" for % — 60°, 
so that any value of x lying between 147° 12' and 157° 12' will give a satisfactory 
explanation of this experiment. Also Cg would be negative. 
When the reflection is polar and the incident light is polarised in the plane of 
incidence, Kujs’dt finds that 0 has the opposite sign to Jq for all angles of incidence. 
The vector angle of A/B cos % is found to be 
and 
cc + 36° 42' when i — 90°, 
ic -b 98° 26' when i — 0°. 
The cosine of this vector angle will be negative for all angles of incidence, provided 
the value of x lie between 53° 18' and 171° 34'. 
The two experiments indicate that for nickel x has a value intermediate between 
147° and 157°. 
The Experiments of Sissingh and Zeemax. 
20. I now pass to a much more precise and accurate test of the present theory, 
the materials for wliich are to be found in the elaborate series of experiments made 
during the last few years at Leyden, by Sissixgh and bv Zeemax. 
