nd it did not. Nor did
the Refractions cause any other sensible Colour than violet to emerge
out of this Light, as they would have done out of white Light, and by
consequence out of this violet Light had it been sensibly compounded
with white Light. And therefore I concluded, that the reason why I could
not see the Species of the Lines distinctly by this Colour, was only
the Darkness of this Colour, and Thinness of its Light, and its distance
from the Axis of the Lens; I divided therefore those Parallel black
Lines into equal Parts, by which I might readily know the distances of
the Colours in the Spectrum from one another, and noted the distances of
the Lens from the Foci of such Colours, as cast the Species of the Lines
distinctly, and then considered whether the difference of those
distances bear such proportion to 5-1/3 Inches, the greatest Difference
of the distances, which the Foci of the deepest red and violet ought to
have from the Lens, as the distance of the observed Colours from one
another in the Spectrum bear to the greatest distance of the deepest red
and violet measured in the Rectilinear Sides of the Spectrum, that is,
to the Length of those Sides, or Excess of the Length of the Spectrum
above its Breadth. And my Observations were as follows.

When I observed and compared the deepest sensible red, and the Colour in
the Confine of green and blue, which at the Rectilinear Sides of the
Spectrum was distant from it half the Length of those Sides, the Focus
where the Confine of green and blue cast the Species of the Lines
distinctly on the Paper, was nearer to the Lens than the Focus, where
the red cast those Lines distinctly on it by about 2-1/2 or 2-3/4
Inches. For sometimes the Measures were a little greater, sometimes a
little less, but seldom varied from one another above 1/3 of an Inch.
For it was very difficult to define the Places of the Foci, without some
little Errors. Now, if the Colours distant half the Length of the
Image, (measured at its Rectilinear Sides) give 2-1/2 or 2-3/4
Difference of the distances of their Foci from the Lens, then the
Colours distant the whole Length ought to give 5 or 5-1/2 Inches
difference of those distances.

But here it's to be noted, that I could not see the red to the full end
of the Spectrum, but only to the Center of the Semicircle which bounded
that end, or a little farther; and therefore I compared this red not
with that Colour which was exactly in the middle