MR. G. A. SCHOTT ON THE REFLECTION AND REFRACTION OF LIGHT. 859 
Elect 1 -omagnetic and Contractile Ether Theories. 
Here the expressions (XT.) for the amplitude and change of phase at retlectioii 
contain four constants A, B, E, F, of which the really effective ones are B, E. The 
constant A in the expression for the ratio of the amplitudes is multiplied by 
cos (^Q + ^\), and thus is without effect at the polarizing angle, at which the deviation 
from Fresnel’s formula is most marked. A cannot therefore be determined with 
any great accuracy, seeing that a considerable change in its value produces only a very 
slight effect on the result. In some cases it may be put = zero without impairing 
the accuracy of the formula. 
The same considerations apply to the constant F in the expression for the phases. 
The other two constants B, E ought to satisfy the condition, E^ = — . B. As regards 
accuracy of determination the order of the constants is E, B, F, A. 
The experiments discussed are those of Jamin on solids and liquids (see his two 
papers, ‘'Ann. de Chimie et Physique,’ serie TIL, 29 (1850) and 31 (1852) ; a series for 
flint-glass by ICuRz Pogg. Ann.,' 108), and some of Quincke’s (‘ Pogg. Ann.,’ 128)). 
Of these the experiments of Jamin are much the best, and are almost as well repre¬ 
sented by the empirical formula of Cauchy as by the theoretical formulee found above. 
This might excite surprise—seeing that Cauchy’s formulae involve only one independent 
constant, the ellipticity e—did we not remember that of the three independent 
constants B, F, A (E of course is not independent), two, F and A, do not have 
much influence on the result. The experiments of Quincke are the most irregular, 
but they are of interest because Quincke investigates the reflection in each other 
from the bounding surface of pairs of media. Of these I have only taken those in 
which there are ten or more different determinations, where there is some chance of 
the constants being accurately determined. The experiments of Haughton (‘ Phil. 
Trans.,’ 1863) I have not had time to consider, hut, with but one or two exceptions, 
his series consist of too few determinations to allow of an accurate determination of 
the constants. 
In all the above cases measurements wei’e made of the difference of phase, by means 
of a Babinet’s compensator, directly, and of the ratio of the intensities, indirectly. 
The polarizer was placed at a large angle a with the plane of incidence, so that in 
the incident beam the component polarized perpendicularly to the plane of incidence 
is of great intensity relative to the parallel component. The azimuth ^ of the 
reflected light was determined. Then B _L/B 11 is given by the equation R _L/R 11 
= tan ZTT = tan y8/tan a. By thi.^ means the determination of is rendered more 
accurate, firstly, because the absolute error in m is made much less than tliat of yd 
owing to the largeness of tan «, and secondly, because the determination of /3 is 
itself more accurate, the intensities of the components in the reflected light being 
more nearly equal. 
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