88 
Dr. Brewster on new properties of heat, 
The terminal and lateral fringes are produced by No. 2, 3, 4, 
when they are turned round 45V Their complementary 
fringes are extremely beautiful. 
When No. 2 is combined with No. 3, they produce fringes 
of contrary flexure like No. 1. The nature and origin of ail 
these fringes are explained in a subsequent Proposition. 
Proposition XXVII. 
If a rectangular plate of crystallized glass which exhibits the 
fringes through its edges is inclined to the polarised ray in a 
plane perpendicular to the direction of the fringes, the central 
tint will descend in the scale as if the plate had increased in 
depth ; but when it is inclined in a plane parallel to the direc- 
tion of the fringes, the tint will ascend in the scale as if the 
plate had diminished in depth . 
The result contained in this Proposition was established by 
the same experiments which are described in Prop. XXIV., 
the fringes seen through the edges of the plate being used 
instead of those seen through its broad surfaces. The effects 
of inclination in these two cases are directly opposite. 
Proposition XXVIII, 
The regularity in the crystallization of a plate of glass according 
to one of its dimensions, is not disturbed by any irregularity of 
its crystallization in another direction. 
If a plate of glass is crystallized from a centre, as in Prop. 
XIX., or if a confused crystallization is induced by cooling it 
at different places, so that no distinct fringes can be seen when 
polarised light is transmitted through the broad surfaces of 
the plate, the fringes seen through its edges will be perfectly 
