w casts the Images of Objects abroad
upon a Sheet of white Paper in a dark Room. The aforesaid white Paper,
erected perpendicular to the Horizon, and to the Rays which fell upon it
from the Lens, I moved sometimes towards the Lens, sometimes from it, to
find the Places where the Images of the blue and red Parts of the
coloured Paper appeared most distinct. Those Places I easily knew by the
Images of the black Lines which I had made by winding the Silk about the
Paper. For the Images of those fine and slender Lines (which by reason
of their Blackness were like Shadows on the Colours) were confused and
scarce visible, unless when the Colours on either side of each Line were
terminated most distinctly, Noting therefore, as diligently as I could,
the Places where the Images of the red and blue halfs of the coloured
Paper appeared most distinct, I found that where the red half of the
Paper appeared distinct, the blue half appeared confused, so that the
black Lines drawn upon it could scarce be seen; and on the contrary,
where the blue half appeared most distinct, the red half appeared
confused, so that the black Lines upon it were scarce visible. And
between the two Places where these Images appeared distinct there was
the distance of an Inch and a half; the distance of the white Paper from
the Lens, when the Image of the red half of the coloured Paper appeared
most distinct, being greater by an Inch and an half than the distance of
the same white Paper from the Lens, when the Image of the blue half
appeared most distinct. In like Incidences therefore of the blue and red
upon the Lens, the blue was refracted more by the Lens than the red, so
as to converge sooner by an Inch and a half, and therefore is more
refrangible.

_Illustration._ In the twelfth Figure (p. 27), DE signifies the coloured
Paper, DG the blue half, FE the red half, MN the Lens, HJ the white
Paper in that Place where the red half with its black Lines appeared
distinct, and _hi_ the same Paper in that Place where the blue half
appeared distinct. The Place _hi_ was nearer to the Lens MN than the
Place HJ by an Inch and an half.

_Scholium._ The same Things succeed, notwithstanding that some of the
Circumstances be varied; as in the first Experiment when the Prism and
Paper are any ways inclined to the Horizon, and in both when coloured
Lines are drawn upon very black Paper. But in the Description of these
Experiments, I have set down such Circumstances, by w