I 
2 06 
On the Polarization of Light . 
[April 
_ A-zimufA of Plane 
f? 3 
_/?ay wholly 
Id all tlifi intei mcdiuts positions oi the second glass there whs 3 partial reflection 
and partial transmission of the light, tlie one increasing as the other diminished, 
like the sine and cosine of the varying angle (figure 3 .) 
The most convenient instrument for shewing this experiment is depicted in 
figure 4 : it consists of a simple telescope tube, closed at both ends with brass* caps, 
having holes perforated in their centres, so as to insulate a small pencil of light! 
To both extremities are adapted glass mirrors, one of which should be capable of 
turning in azimuth round the axis of the tube- 
2 . The only angle at which glass perfectly polarizes light bv reflection from 
its outer surface, is, according to Biot, 35° 25'*. The under surface is Mud, by 
Malms, to enjoy the same property, but at a different angle, dependin'- upon the 
refracting power of the glass ; thus light impingingupon the glass he an 
angle ot do 2 o , was refracted so as to form an angle of 57 ° 6' with thj(bi#&' sur- 
face. By beveling one edge of the glass to the complement of this angE 32° 54 ' 
so that the ray should emerge without undergoing a new refraction, or perpen! 
11 T l0 T perfectly polarized. A prism, containing two angles of 
-32° 54 , may be used m lieu of the second redactor in figure 4. 
7 
refleC t*Seth°e f T W* flL 
taed. Bi0t #nd f0 " nd thCSe 
m£ K!” 4 .. 7 . 7 ::..:: f ; % and *"***» - 1,3359 
Amber,.. 33 25 *>4666 
Sulphate Barytes, . .’.* 32 06 
Topaz, ^ 31 oo i,o4zS 
N ative Sulphur, 20 00 ^ » ®**20 
Diamond, " 22 54 2,0278 
4. From tliese experiments Brewster deduced n , , 2,43905 
the polarized ray reflected from a?ty surface is a n,r . 'T r ' / UW naineI - v > that 
portion of the incident ray, (figure 6-f Where’ the feftSv™^ *°x the re f racte4 
the angle of polarization will become 45 •> fti ffUre 7) J c . x ° n ' Wishes, as in air, 
When on the contrary the refraction is infinite' 5 tlie Jn , it can never exceed. 
0° (figure 8-j ignite, the angle of polarization becomes 
5. Hitherto we have noticed the portion hf . , - 
glass at 35° 25': but of the whole ray which arrives fitldk ***£? the surface of 
suffers reflection • the remaining half passes through the 4 Ts and 006 ** °$ 
transmission, to be completely nolarized in a c . <= iass > ^nd proves, after 
imir. A little reasoning will supply the ’cause of 'thisTfofereri^n °/ '*1®, re " ected 
* every natural luminous 
* Brewster makes this ancle 34° n, - 
ceed best. Probably the diiicrence isdut **,23* le 
