66 Dr. Brewster on new properties of heat, 
instead of the brownish red, and the brownish red instead of the 
green . 
The same result was obtained by combining glass plates 
crystallized in these tw r o different w'ays. 
In order to obtain a still more uniform temperature, I took 
a parcel of 15 crown glass plates, and suspended them in a 
vessel of boiling water, at some distance from the bottom- 
As soon as they had acquired the temperature of the water, I 
lifted them out, and placed them with their edges on a cold 
iron. The black spaces and fringes immediately appeared, 
and a yellow tint was visible in the middle of the interior 
fringes. The interior fringes had the same properties as the 
exterior fringes described in Prop. VIII. and vice versa. This 
experiment was frequently repeated with the same result. 
The fringes produced in this manner, we shall call the 
unusual series of fringes, in opposition to the usual series, or 
those produced by placing cold glass upon a hot iron. 
I was now anxious to observe the phenomena that would be 
presented by inducing the unusual series of fringes upon a 
parcel of plates that already possessed the usual series. In 
order to effect this, I placed the parcel of 1 5 plates of glass, 
already mentioned, with their edges on the bottom of a vessel 
filled with boiling water. 
The bottom of the vessel being very hot, communicated to 
the parcel of plates the usual series of fringes, just like a plate 
of hot iron. When the parcel was taken out and placed 
upon a cold iron, the usual series of fringes was distinctly seen ; 
but after the lapse of some seconds, it gradually disappeared, 
and was displaced by the unusual series advancing from the 
edges, and occasioned by the cooling of the plates. The 
