Laws of Reflexion from Metals. 



61 



found for a great number of metals by Sir David Brewster. 

 The following Table is computed for steel, taking M = 3, 

 X - 54. 



The most remarkable thing in this Table is the last column, 

 which gives the intensity of the light reflected when common 

 light is incident. The intensity decreases very slowly up to a 

 large angle of incidence (less than 75), and then increases up to 

 90, where there is total reflexion. This singular fact, that the 

 intensity decreases with the obliquity of incidence, was dis- 

 covered by Mr. Potter, whose experiments extend as far as an 

 incidence of 70. Whether the subsequent increase which ap- 

 pears from the Table indicates a real phenomenon, or arises from 

 an error in the empirical formulae, cannot be determined without 

 more experiments. It should be observed, however, that in these 

 very oblique incidences Fresnel's formulae for transparent media 

 do not represent the actual phenomena for such media, a great 

 quantity of the light being stopped, when the formulas give a 

 reflexion very nearly total. 



The value S' - 8, or the difference of phase, increases from 

 to 180. When a plane-polarized ray is twice reflected from 

 a metal, it will still be plane-polarized if the sum of the values 

 of & S for the two angles of incidence be equal to 180. 



It appears from the formulae that when the characteristic \ 

 is very small, the value of 8' will continue very small up to the 



