362 Mr. Brougham's Experiments and Observations 
bably be afterwards found to be the case ; in the mean time 
there is little doubt that the sizes are the cause of the fact. 
II. 
Several phenomena are easily explicable on the principles 
just now laid down. 
1. If a pin, hair, thread, &c. be held in the rays of the sun 
refracted through a prism, extending through all the seven co- 
lours, a very singular deception takes place : the body appears 
of different sizes, being largest in the red and decreasing gra- 
dually towards the violet. This appearance seemed so extra- 
ordinary, that some friends who happened to see it as well as 
myself, suspected the body must be irregular in its shape. On 
inverting it, however, the same thing took place; and on turn- 
ing the prism on its axis, so that the different rays successively 
fell on the same parts, the visible magnitude of the body varied 
with the rays that illuminated it. This appearance is readily 
accounted for by the different reflexity of the rays, and follows 
immediately from Obs. 2. and 3. 
2. Sir Isaac Newton found that the rings of colours made 
by thin plates and by thick plates of glass (as he calls them), 
when formed of homogeneal light, varied in size with the rays 
that made them, being largest in the most flexible rays. I 
have had the pleasure of observing several other sorts of rings, 
so extremely similar, and formed by flexion, that I can no 
longer doubt of this being also the cause of the phenomena 
observed by Newton. I shall first describe a species, to prove 
“ that the colours by thick and thin plates are one and the 
“ same phenomenon, only differing in the thickness of the 
