408 NEUMANN ON A METHOD OF ESTIMATING THE 
face having its axis directed towards the point of section, the plane 
of incidence lies on my right-hand. This being determined, my 
observations are as follows; @ indicating the azimuth of polar- 
ization of the incident beam, and « that of the reflected. 
Incidence 45°, azimuth of the plane of incidence +90. 
1. The extraordinary ray disappeared when a was = —65° 25!. 
2. The ordinary ray disappeared when @ was = + 22° 28! 
2, . swhenx. a=) 4,0, awas =— 2° 24!, 
4 ns a=) 90; a gy = Be ee 
5. or n=O; Gg == 1s 
Bite ioe Te ome) 050, @ 4» = 87° 23!. 
| a ee a 5 =+89° 575. 
8. as a= +20° 29', a», =—46° 30: 
go geese ag») al t= toes 
10. 5 @=—45° @ 5 =+64°19!. 
1, ye ae’, a = — 70° ae 
We thus obtain the following equations :— 
1. —o'tan 65° 25! 4+ o! =0. 
2. a! tan 22° 28! + o! = 0. 
3. —tan 2° 24! = . 
4, tan 84°93! =F 
oO 
— ptan6° 19! + s! = 0. 
; p! tan 87° 23'+ s = 0. 
ptan 89° 57'5 +38! | 
p' tan 89° 57"5+s8 
— ptan 46° 30'+8' 
— p! tan 46° 30’ +s" 
p tan 53° 33'+s! 
p tan 53° 33'+s° 
© j9! 
10, jeter?) SE eee 
p' tan 64° 19'+s 
_ —ptan 70° 23'+8" | 
~ — p' tan 70° 23'+s 
I find from these 11 equations, 
w! = — o! cot 22° 28', and p = — s tan 22° 30/. 
ow! = + o cot 65° 25', and p! =— stan 2°32. 
s'=— stan 2°31! 
for) 
VP tan 83° 55!= 
8. tan 20° 29'= 
9, —tan32°39'= 
11. tan 45° 
