230 . On Polarization of Light by Refraction. 
: in- ’ nf 64; Batuttan ah i = ’ 
pore a dae | served. poms ele 
= | OF 0° 0 | 45° OF 
10 6 363} 0 13 | 45 13 | 45 6 
20 |13 5 | O 27145 27°) 45 25 
-25. {16.15 | 04-82 | 4532-145 40 
30. | 19 20 | 0.40 | 45 40} 46 0 
35, | 22 19 | 1 12 | 46 12 | 46 25 
40 |25 10 | 1 30 | 46 30 | 46 56 
45 (27 55 | 1 42 | 46 47 | 47 34 
50 | 30 29 | 2 48 | 47 42 | 48 24 
55 52 | 3 54 | 48. 54 | 48 59 
60- | 85 -01 5.2 9 1.60.,.7.|. 50...36 
65 | 36 63 | 6.48 (|-61 48 152 7 
70 | 38 29] 8. 53-7 | 53 59 
75.| 39 45 | -9. 55 | 54 55. | 56 18 
80. | 40 42 | 12 10| 57 10|59 5 
85 | 41 .17 | 15 45 | 60 45 | 62 24 
86 | 41 21116 391/61 39/63 9 
90 | 41 28 66 19 
The last column but one of the Table was calculated by the bee 
mula, 
Cot 4=(cos (i — i‘)? 
n-being in this case 2.. The conformity of the observed wie 
calculated results is sufficiently great, the average difference’ being 
only 41’. The errors however being almost all negative, I suspect- 
ed that there was an error of adjustment in the apparatus; and 
upon repeating the experiment at 80°, the point of maximum error, 
tantae. the inclination was fully 58° 40’, giving a difference only 
of 25’ in place of 1° 55’, I did not think it necessary to repeatall 
the observations ; but I found, by placing the analysing rhomb at the 
calculated tntlioetions, that the extraordinary image invariably =— 
peared, the best of all proofs of the correctness of the formula. 
In these experiments r=45° and cot =1; but in order to try 
the formula when z varied from 0° to 90°, I wk the case where the 
angle of incidence was 80° and »=58° 40’ when «=45°. The 
following were the results, oe: 
