polarisation of light by reflexion from transparent bodies. 139 
© 1 
Polarising angle for the second surface of diamond 21 59 
Angle at which total reflexion commences - 23 46 
Difference i° 47' 
Sect. III. On the laws of the polarisation of light by reflexion 
from the separating surfaces of different media. 
Although the attention of Malus was directed to this branch 
of the subject, yet he does not appear to have obtained even a 
single measure of the angles at which light is polarised at the 
separating surfaces of different media. “ After having de- 
“ termined, “ he observes/’ the angles under which polarisa- 
“ tion takes place with respect to different bodies, water and 
“ glass , for example, I sought for that at which the same 
“ phenomenon would take place at their surface of separation, 
“ when they are in contact, but the law according to which 
“ this last angle depends upon the first two still remains to 
“ be discovered.” I have often attempted the same experi- 
ment with the same want of success, but besides being unable 
to determine the law, I could never fmd that there was any 
maximum angle of polarisation at the common surface of 
water and glass, when the light was incident from air. It is 
curious to remark, that Malus does not say, that such an 
angle existed although this may be considered as implied in 
the observation that the law still remains to be determined. 
Now it is sufficiently singular, as will appear from the follow- 
ing propositions, that there is no angle of incidence at the 
first surface of the water which will admit the light to be pola- 
rised at the common surface of the water and the glass. 
