on the Affections and Properties of Light. 355 
in the former rays than in the latter) ; and this agrees with an 
observation of Sir Isaac Newton, as far as he tried it, which 
was with respect to deflexion. In making several experiments 
with prisms, I hit on a very remarkable confirmation of this. 
I observed on each side of the spectrum four or five distinct 
fringes, like the images by reflexion, coloured in the order of 
the spectrum, but quite well defined at the edge, and eveiv 
pretty distinct at the end ; they were also much narrower than 
those images, but like them they inclined much to the violet, 
and were broadest in the red, growing narrower by degrees, 
and narrowest of all in the violet. I moved the prism and 
they disappeared, but when the prism was brought back to its 
former position, they also returned. I then observed the prism 
in open light, and saw that it had veins, chiefly opaque and 
white, running through it, and that there were several of these 
in the place where the light passed when the prism was held 
as before. But in case the inclination and shape of these images 
might be owing to the irregular order in which the veins were 
laid, I held another prism, which happened to have parallel 
veins ; in many positions of this the fringes or images re- 
turned, not indeed always so regular nor always of the same 
kind ; for some were confused and broader, formed (as I con- 
cluded from this and their position) by reflexion ; others made 
by transparent veins and air-bubbles were also irregular, but 
inclined to the red, the violet being farthest from the perpen- 
dicular, and these were obviously caused by refraction ; yet all 
agreed in this, that they were broadest in the red, and nar- 
rowest in the violet parts. 
Observation 5. I held, in the direct rays of the sun at \ an inch 
from the small hole in the window-shut, a glass tube, free from 
mdccxcvii. 3 A 
