150 Dr. Brewster on the laws which regulate the 
The particle -{- ~ will represent a particle so completely po- 
larised in a positive manner, that it will be polarised by re- 
flexion at o° of incidence ; — will represent a particle so 
completely polarised in a negative manner that it will be po- 
larised by reflexion in an opposite plane at o° of incidence ; + 
a particle so far polarised that it will require only a re- 
flexion at i° of incidence to complete its polarisation, and so on 
with all the other particles till we come to , » which is a 
particle of direct light so completely unpolarised that it requires 
to be reflected at the maximum polarising angle before it can 
suffer complete polarisation. 
This peculiar state of the rays before they fall upon a trans- 
parent body might have been deduced a priori by considering 
that when a mass of particles is projected from a self-lumi- 
nous body, the different sides of the rays, or poles of the 
luminous particles must have every possible position relative 
to the direction of their motion, which is the state described 
in the Proposition. If we break a tourmaline, for example, 
into a number of fragments, there will be a positive and a 
negative electrical pole in every possible direction, and a mass 
of moving tourmalines will have, nearly, the same relation to 
the tourmaline itself in which all the axes are regularly arrang- 
ed, as a beam of direct has to a beam of polarised light. 
Corollary 1 . A beam of light that has suffered reflexion at 
any angle above o°, will be in a state which may be repre- 
sented in the following manner, the angle of incidence being 
supposed to be 4, 0 . 
