SALV. I ſee already, whither the apprehenſion of Sagredus,
a moſt diligent obſerver of Natures ſecrets, tendeth; and I
would lay any wager, that amongſt the thouſands that have
ſerved Cats to contract and inlarge the pupils of their eyes very
much, there are not two, nor haply one that hath obſerved the
like effect to be wrought by the pupils of men in ſeeing, whilſt
the medium is much or little illumin'd, and that in the open light
the circlet of the pupil diminiſheth conſiderably: ſo that in
king upon the face or Diſcus of the Sun, it is reduced to a
neſſe leſſer than a grain of ^{*} Panick, and in beholding objects
that do not ſhine, and are in a leſſe luminous medium, it is
god to the bigneſſe of a Lintel or more; and in ſumme this
expanſion and contraction differeth in more than decuple
portion: From whence it is manifeſt, that when the pupil is
much dilated, it is neceſſary that the angle of the rayes
courſe be more remote from the eye; which happeneth in
holding objects little luminated. This is a Doctrine which
gredus hath, juſt now, given me the hint of, whereby, if we
were to make a very exact obſervation, and of great
quence, we are advertized to make the obſervation of that
courſe in the act of the ſame, or juſt ſuch another operation; but
in this our caſe, wherein we are to ſhew the errour of
mers, this accurateneſſe is not neceſſary: for though we ſhould,
in favour of the contrary party, ſuppoſe the ſaid concourſe to be
made upon the pupil it ſelf, it would import little, their miſtake
being ſo great. I am not certain, Sagredus, that this would have
been your objection.
a moſt diligent obſerver of Natures ſecrets, tendeth; and I
would lay any wager, that amongſt the thouſands that have
ſerved Cats to contract and inlarge the pupils of their eyes very
much, there are not two, nor haply one that hath obſerved the
like effect to be wrought by the pupils of men in ſeeing, whilſt
the medium is much or little illumin'd, and that in the open light
the circlet of the pupil diminiſheth conſiderably: ſo that in
king upon the face or Diſcus of the Sun, it is reduced to a
neſſe leſſer than a grain of ^{*} Panick, and in beholding objects
that do not ſhine, and are in a leſſe luminous medium, it is
god to the bigneſſe of a Lintel or more; and in ſumme this
expanſion and contraction differeth in more than decuple
portion: From whence it is manifeſt, that when the pupil is
much dilated, it is neceſſary that the angle of the rayes
courſe be more remote from the eye; which happeneth in
holding objects little luminated. This is a Doctrine which
gredus hath, juſt now, given me the hint of, whereby, if we
were to make a very exact obſervation, and of great
quence, we are advertized to make the obſervation of that
courſe in the act of the ſame, or juſt ſuch another operation; but
in this our caſe, wherein we are to ſhew the errour of
mers, this accurateneſſe is not neceſſary: for though we ſhould,
in favour of the contrary party, ſuppoſe the ſaid concourſe to be
made upon the pupil it ſelf, it would import little, their miſtake
being ſo great. I am not certain, Sagredus, that this would have
been your objection.
SAGR. It is the very ſame, and I am glad that it was not
together without reaſon, as your concurrence in the ſame
reth me; but yet upon this occaſion I would willingly hear what
way may be taken to finde out the diſtance of the concourſe of
the viſual rayes.
together without reaſon, as your concurrence in the ſame
reth me; but yet upon this occaſion I would willingly hear what
way may be taken to finde out the diſtance of the concourſe of
the viſual rayes.
SALV. The method is very eaſie, and this it is, I take two
long^{*} labels of paper, one black, and the other white, and make
the black half as broad as the white; then I ſtick up the white
gainſt a wall, and far from that I place the other upon a ſtick, or
other ſupport, at a diſtance of fifteen or twenty yards, and
ding from this, ſecond another ſuch a ſpace in the ſame right line,
it is very manifeſt, that at the ſaid diſtance the right lines will
concur, that departing from the termes of the breadth of the
white piece, ſhall paſſe cloſe by the edges of the other label
ced in the mid-way; whence it followeth, that in caſe the eye
were placed in the point of the ſaid concourſe or interſection,
the black ſlip of paper in the midſt would preciſely hide the
long^{*} labels of paper, one black, and the other white, and make
the black half as broad as the white; then I ſtick up the white
gainſt a wall, and far from that I place the other upon a ſtick, or
other ſupport, at a diſtance of fifteen or twenty yards, and
ding from this, ſecond another ſuch a ſpace in the ſame right line,
it is very manifeſt, that at the ſaid diſtance the right lines will
concur, that departing from the termes of the breadth of the
white piece, ſhall paſſe cloſe by the edges of the other label
ced in the mid-way; whence it followeth, that in caſe the eye
were placed in the point of the ſaid concourſe or interſection,
the black ſlip of paper in the midſt would preciſely hide the