230 



On Polarization of Light by Refraction. 



The last column but one of the Table was calculated by the for- 

 mula, 



Cot ^ = (cos(i-i'))=' 

 n being in this case 2. The conformity of the observed with the 

 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, 

 I found that the inclination was fully 58° 40', giving a difference only 

 of 25' in place of 1° 55'. I did not think it necessary to repeat all 

 the observations ; but I found, by placing the analysing rhomb at the 

 calculated inclinations, that the extraordinary image invariably disap- 

 peared, the best of all proofs of the correctness of the formula. 



In these experiments x=45° and cot x=l ; but in order to try 

 the formula when x varied from 0° to 90°, I took the'case where the 

 angle of incidence was 80° and 9 = 58° 40' when a: =45°. The 

 following were the results. 



