204 On Refraction. 
and form a beautiful spectrum on the opposite wall, orange at 
the bottom, violet at the top, with intermediate colours :’ but on 
looking through the same refracting angle at the hole in the 
pasteboard or window-shutter, the experimenter is surprised to 
find all the colours reversed, violet at the bottom, orange at the 
top. Newton must have had very defective eyes, or must have 
been very inattentive, entirely to have overlooked this interesting 
fact; for we often find him in the Optics looking at the hole 
through the prism, yet never mentioning it. I shall explain this 
phenomenon in my treatise on Vision, with which it is intimately 
connected ; and shall merely remark, that the rays forming the 
spectrum have nothing to dowith vision-making images. ‘*Then,” 
says Newton, ‘I looked through the prism upon the hole. 
In this situation, viewing through the said hole, I observed the 
length of its refracted image to be many times greater than its 
breadth, and that the most refracted part thereof appeared vio- 
let, the least refracted red, the middle parts blue, green and 
yellow in order. The same thing happened when I removed the 
prism out of the sun’s light, and looked through it upon the hole 
shining by the light of the clouds beyond it; and yet, if the re- 
fractions were done regularly, according to one certain proportion 
of the sines of incidence and refraction, as is vulgarly supposed, 
the refracted image ought to have appeared round.” Here 
Newton’s attention seems to have been so completely absorbed’ 
with preconceived opinions, that he never noticed the colours 
being reversed ; and consequently, that the image he saw on the 
plane of the prism and that on the opposite wall were distinct 
and different, bearing no analogy whatever. On looking at the 
hole in the window-shutter through the lower refracting angle, 
we are obliged to direct the optic axis on a line with the ground, 
and then see a reflected and not a refracted image painted on the 
prismatic plane. 
As I have shown in the first volume of the Experimental Out- 
lines for a new Theory of Vision, Light, and Colours, p. 48, that 
Newton never separated what he calls white light into seven co- 
loured rays, I think it perfectly unnecessary to speak of their dif- 
ferent refrangibilities: any fluid passing through a resisting me- 
dium obliquely must be lengthened; and I have shown that a 
straight stick, when viewed through the prism, is curved ; there- 
fore it is not surprising that the image of the hole should be ob- 
long, not circular, and bounded by two semicircular ends. 
Here I think it necessary to mention, that when writing the 
Outlines I had not made the first experiment mentioned in this 
paper, and therefore believed in the theory of refractions. The 
next experiment on which the theory of refraction seems to rest, 
is the following: “ Take an empty vessel, such as a basin, and all 
along 
