OF THE REFLECTION AND REFRACTION OF LIGHT. 
709 
It is remarkable that in this case the two components introduced by reflection are 
the same, whether the vibration be in, or perpendicular to, the plane of incidence. 
Comparing this method of obtaining the effects of reflection from a magnetised 
surface with that given by me in the ‘Proceedings of the Poyal Society for 1876,’ 
No. 176, it is to be observed that my equations (I) and (II) are unaltered if the signs 
of v and rj are both reversed together, or if those of v and ^ and £ are all reversed, 
showing that a circularly polarised ray in one direction is reflected according to the 
same laws when the magnetisation is one way as the oppositely circularly polarised 
ray would be if the magnetisation were reversed, and hence my former method of 
dividing the incident plane polarised ray into two opposite circularly polarised ones, 
each of which was reflected according to its own laws, is j ustified. 
In comparing these expressions with the results of Mr. Kerr’s admirable experiments, 
it is necessary to observe, as I mentioned before, that the introduction of a difference 
of phase between the reflected components is a question of a different order from that 
here discussed, and probably to some extent at least depends on the want of abrupt¬ 
ness in the change from one medium to the other. For instance, my expressions give 
no change of plane of polarisation when light is reflected normally from the end of a 
magnet, but they would lead one to expect that the only effect was a slight elliptic 
polarisation, the major axis of the ellipse being in the same plane as the original plane 
of polarisation. Now Mr. Kerr’s experiments show that there is some rotation of this 
plane by reflection, and a supposition similar to one long ago proposed to explain the 
known elliptic polarisation of metallic reflection—namely, that the efficient reflecting 
surface has some depth—may easily be shown to lead to Mr. Kerr’s result. On this 
hypothesis the reflected ray is the resultant of the rays reflected from a small thick¬ 
ness at the surface of separation of the media ; and in the case of normal reflection 
from the end of the pole of a magnet, each of these components would be slightly 
turned from its original plane of polarisation owing to having passed through a very 
small thickness of a very powerful rotatory polarising substance—namely, this super¬ 
ficial layer of the magnet—hence it is evident that their resultant would no longer be 
polarised in the same plane as the incident ray. I only give this as an instance of 
how this question of a difference of phase affects the results, and how the hypotheses 
that have been framed to explain it might be used to bring my results into complete 
accord with Mr. Kerr’s experiments. I hardly think it worth while going into this 
more fully, as it is treading so closely upon unknown ground—namely, the connexion 
between matter and ether—that our hypotheses are to a great extent merely 
conveniences. 
Another question is the extent to which y affects ordinary reflection from a power¬ 
fully magnetic substance like iron. I have never come across any experiment tending 
to show that the reflection from iron was at all peculiar. This may be owing to the 
electrostatic inductive capacity being a characteristic of the ether in the matter, while 
magnetic inductive capacity is a characteristic of the matter, and so only affects the 
MDCCCLXXX. 4 Y 
