qj 6 Mr. Brougham's Experiments and Observations on 
be owing to the plates of air between them, appear to have a 
different cause, as may be without much reasoning gathered 
from the curious experiments of the Abb£ Mazeas,* and even 
from one or two of Sir Isaac's own, in which he supposes 
some medium more subtile than air to be between the glasses.'f 
But at present I forbear entering into the subject any farther : 
this paper has been already extended to a greater length than 
was at first intended. And I hasten to conclude, by a short 
summary of Propositions, containing the principal things 
which have been demonstrated in the course of it. 
Prop. I. The angles of inflection and deflection are equal, 
at equal incidences. 
Prop. II. The sine of inflection is to that of incidence in a 
given ratio (which is determined in the paper.) 
Prop. III. The sun's light consists of parts which differ in 
degree of inflexibility and deflexibility, those which are most 
refrangible being least flexible. 
Prop. IV. The flexibilities of the rays are inversely as their 
refrangibilities ; and the spectrum by flexion is divided by the 
harmonical ratio, like the spectrum by refraction. 
Prop. V. The angle of reflection is not equal to that of in- 
cidence, except in particular (though common) combinations 
of circumstances, and in the mean rays of the spectrum. 
Prop. VI. The rays which are most refrangible are least 
reflexible, or make the least angle of reflection. 
Prop. VII. The reflexibilities of the different rays are in- 
versely as their refrangibilities, and the spectrum by reflection 
is divided in the harmonical ratio, like that by refraction. 
* Mem. de V Academie pour Vannee 1738. 
f Optics, Book II. Part I. Obs. xo and 11. 
