272 Mr. Brougham’s Experiments a;: 1 Observations on 
some continuation of experiments and obs vations which may 
relieve us from the necessity of the supposit on. My specula- 
tions on this subject have by no means been completed, as I 
have not yet finished the demonstrations and experiments into 
which it has engaged me to enter ; but, in order to complete my 
plan, I shall offer a few hints on the subject. The parts of light 
are affirmed, in Prop. III. Book I. Part I. of the Optics, to be 
different in reflexibility; that is, according to the author's de- 
finition, in disposition to be turned back, and not transmitted 
at the confines of two transparent media. That the demonstra- 
tion involves a logical error appears pretty evident. When 
the rays, by refraction through the base of the prism used in 
the experiment, are separated into their parts, these become 
divergent, the violet and red emerging at very different angles, 
and these were also incident on the base at different angles, 
from the refraction of the side at which they entered ; when, 
therefore, the prism is moved round on its axis, as described in 
the proposition, the base is nearest the violet, from the position 
of the rays by v refract ion, and meets it first ; so that the violet 
being reflected as soon as it meets the base, it is reflected be- 
fore any of the other rays, not from a different disposition to 
be so, but merely from its different refrangibility ; although 
then this experiment is a complete proof of the different re- 
frangibility of the rays, it proves nothing else ; and indeed an 
experiment will convince us, that the rays all have the same dis- 
position to be reflected, provided the angle of incidence be the 
same. For I held a prism vertically, and let the spectrum of 
another prism be reflected by the base of the former, so that 
the rays had all the same angle of incidence ; then turning 
round the vertical prism on its axis, when one sort of rays 
