604 
MR. R. T. GLAZEBROOK ON THE REFRACTION OE PLANE 
and 
Also 
XEi = XR 3 =XR, 
angle !RjXM=60 o 
whence 
B 1 M=JB 1 R 3 =35 r ° 28' 
and 
R 1 X=44° 37' 
XM=26° 15' 30' 
Thus 
BX=63° 44' 30". 
and EX is the angle denoted by f3 in the formulae. 
Again we have 
R 3 P~0 p 50' 
Therefore 
MP'=36° 38' 
In the arc P / E 1 take P'A=90°. 
Then B A is the trace of the face of incidence, and 
X=ABX=AM=90 o -MP'=53° 22' 
These values of /3 and X were used in reducing the experiments. 
The error produced by assuming P, Itj, B 3 , and Q to be in the same zone will be 
discussed later. 
The results of the experiments are contained in the following tables. 
Table I. is the interpolation table used as described above to find <f>" from the value 
of (f>, and gives the series of corresponding values of <f>, <j> and <£"—</>'. 
Table II. gives the values of <j>, and 0 for the case in which the ordinary wave only 
traversed the crystal. 
(f> is directly observed, <£' and 0 are found from the formula 
sin cj)'= sin <£///. 
and 
cot 0 = tan (3 cos (X-j-^) sec (<£—<£') 
where /*= 1-662, /3=6 3° 44' 30", X=53° 22'. 
The values are arranged in pairs. In the first experiment recorded in each pair 
there was no sugar cell in the path of the light. In the second experiment the sugar 
cell was interposed. The fifth column gives the differences between the two values of 
0 thus found, and this, if the formula given by theory were correct, ought to be the 
rotation of the plane of polarization produced by the sugar cell. 
