Dr. Brewster on new properties of heat , &c. 47 
first order of Newton's scale ( Opticks , B. II. Part II.) ; but I 
have since discovered a method of rendering them in every 
case visible, by their effects in modifying the colour of a standard 
plate of sulphate of lime. 
The results of these experiments, while they confirm the 
supposition which I had made, have also led to the discovery 
of many singular phenomena, which constitute a new branch 
of physics, analogous in its general character to the sciences 
of magnetism and electricity. The curious properties of light 
and heat, which are explained in the following paper, and the 
new views which are unfolded respecting the structure of cry- 
stallized bodies, will I trust, attract the notice of the chemist, 
the mineralogist, and the natural philosopher; while the variety 
and splendour of the phenomena which it embraces, will 
recommend it to the attention of those, who value scientific 
researches merely as subjects of exhibition or amusement. 
Sect. I. On the transient effects exhibited during the propagation 
of heat along plates of glass, or during its communication from 
glass to surrounding bodies. 
Proposition I. 
When heat is propagated along a plate of glass , its progress is 
marked by the communication of a crystalline structure, which 
changes its character with the temperature , and which vanishes 
when the heat is uniformly diffused over the plate . 
If we lay the edge of a plate of glass upon a bar of red 
hot iron placed horizontally, and transmit through it a ray of 
light polarised in a plane inclined 45 0 to the horizon, the light 
will be depolarised in various degrees in different parts of the 
glass. When the temperature is made uniform, the glass plate 
loses its property of depolarisation. In order to prove that an 
