on some Applications of it to important Optical Phcenomena. 1 77 



in the photometer at the incidences given in the first and se- 

 cond columns of the following Table; the third and fourth 

 give the quantities of light reflected ; and the fifth the ratio of 

 these quantities, the smaller one being taken as unity. 



With the red light I obtained as in the next Table. The 

 ratio of the intensities of the bright to the dark rings is here 

 much greater than with the green light. I had expected it 

 to be so in some degree, from the greater purity of the light, 

 but not nearly to the extent which 1 found it. I repeated the 

 first trials I made, very often, before I noted them down, and 

 did not do so- until I found clearly that the eye was not satis- 

 fied with any less difference. 



To calcuhite the intensity of the light in the third and 

 fourth columns, I have used the foruuila which I have found 

 for crown glass in the essay above referred to; namely, of every 



100 rays incident, those reflected are equal to c + 



where «, h, c and r, are constant quantities, and /• = 100, 

 fl = 2-7; b = 1-0 1-, and c' = 76; x being variable, anil the 

 sine of incidence to radius as 100. 



T/iiid Scries. Vol. 1. No, 3. Sept. 18JJ. 2 A 



