150 Professor ForseEs on the Refraction 
Mean at 0°...6°.9 
180°...7 .0 
Mean, . 6. 
9 : ‘ 
Mean at 90° and 270°,. 5.6 | Ratio 100 : 81, or 19 per cent. polarized. 
The general concordance of these experiments will be gather- 
ed from the following list of results. 
37. With non-luminous heat from brass about 700° ; ratio of 
effect, when plates E and F were parallel and crossed, 100 : 78; 
100 : 76; 100:80*; 100: 81 (from five observations each), with 
plates E and A (from three observations each), 100 :74; 100: 59; 
100 : 68; 100 : 60; with A and B, ratios 100 : 78; 100: 72. 
38. With non-luminous heat frem mercury, about 500°, plates 
FE and F; 100: 77; 100: 90, plates E and A; 100: 88; with 
A and B, 100 : 78. 
39. But even with heat from water below the boiling point. 
I was able, by the improved method of observing the galvanome- 
ter, art. (5), (6), to establish completely the polarizing effect. One 
series of six comparisons (conducted as in (20),) gave for the pro- 
portions of heat transmitted, when the plates E and F were 
parallel and crossed, 100 : 93; another of eight comparisons, gave 
100 : 96; a third, of eight, 100: 92. Among these twenty-two 
comparisons, only oxe gave a result slightly negative. 
40. With platinum rendered incandescent by alcohol, the ef- 
fect appears decidedly greater than with any other source of heat 
I have tried. Plates E and F; ratios of effect when parallel and 
crossed, 100 : 59; 100 : 62; 100: 66; 100: 54. The brilliancy 
of the incandescence affects materially the transmission. 
41. Alcohol flame, as might be anticipated, is less steady ; 
means from sets of five observations, with plates E and F; 
100 : 66; 100: 72; 100: 79; 100: 42; 100: 62. 
42. With the simple oi/-lamp of Locatelli; plates E and 
F, the ratios are 100 : 76; 100 : 73.5; 100 :'79. 
* Plate B was used to polarize in this experiment. 
