1the ſaid irradiation of four inches to a circle that hath but two
ches of diameter onely, the diameter of the irradiation or
land would be ten inches, and the ſuperficial content of the circle
would be to the area of the naked body, as 100. to 4. for thoſe
are the ſquares of 10. and of 2. the agrandizement would
fore be 25. times ſo much; and laſtly, the four inches of hair or
fringe, added to a ſmall circle of an inch in diameter, the ſame
would be increaſed 81. times; and ſo continually the
tions are made with a proportion greater and greater, according
as the real objects that increaſe, are leſſer and leſſer.
ches of diameter onely, the diameter of the irradiation or
land would be ten inches, and the ſuperficial content of the circle
would be to the area of the naked body, as 100. to 4. for thoſe
are the ſquares of 10. and of 2. the agrandizement would
fore be 25. times ſo much; and laſtly, the four inches of hair or
fringe, added to a ſmall circle of an inch in diameter, the ſame
would be increaſed 81. times; and ſo continually the
tions are made with a proportion greater and greater, according
as the real objects that increaſe, are leſſer and leſſer.
Superficial
gures encreaſing
proportion double to
their lines.
gures encreaſing
proportion double to
their lines.
SAGR. The doubt which puzzled Simplicius never troubled
me, but certain other things indeed there are, of which I deſire
a more diſtinct underſtanding; and in particular, I would know
on what ground you affirm that the ſaid agrandizement is alwayes
equal in all viſible
me, but certain other things indeed there are, of which I deſire
a more diſtinct underſtanding; and in particular, I would know
on what ground you affirm that the ſaid agrandizement is alwayes
equal in all viſible
Objects the more
vigorous they are
in light, the more
they do ſeem to
creaſe.
vigorous they are
in light, the more
they do ſeem to
creaſe.
SALV. I have already declared the ſame in part, when I ſaid,
that onely lucid objects ſo increaſed, and not the obſcure; now I
adde what remaines, that of the reſplendent objects thoſe that are
of a more bright light, make the reflection greater and more
ſplendent upon our pupil; whereupon they ſeem to augment
much more than the leſſe lucid: and that I may no more inlarge
my ſelf upon this particular, come we to that which the true
ſtris of Astronomy, Experience, teacheth us. Let us this evening,
when the air is very obſcure, obſerve the ſtar of Jupiter; we
ſhall ſee it very glittering, and very great; let us afterwards look
that onely lucid objects ſo increaſed, and not the obſcure; now I
adde what remaines, that of the reſplendent objects thoſe that are
of a more bright light, make the reflection greater and more
ſplendent upon our pupil; whereupon they ſeem to augment
much more than the leſſe lucid: and that I may no more inlarge
my ſelf upon this particular, come we to that which the true
ſtris of Astronomy, Experience, teacheth us. Let us this evening,
when the air is very obſcure, obſerve the ſtar of Jupiter; we
ſhall ſee it very glittering, and very great; let us afterwards look
through a tube, or elſe through a ſmall trunk, which clutching the
hand cloſe, and accoſting it to the eye, we lean between the palm
of the hands and the fingers, or elſe by an hole made with a ſmall
needle in a paper; and we ſhall ſee the ſaid ſtar diveſted of its
beams, but ſo ſmall, that we ſhall judge it leſſe, even than a
eth part of its great glittering light ſeen with the eye at liberty:
we may afterwards behold the Dog-ſtars beautiful and bigger than
any of the other fixed ſtars, which ſeemeth to the bare eye no
great matter leſſe than Jupiter; but taking from it, as before, the
irradiation, its Diſcus will ſhew ſo little, that it will not be
thought the twentieth part of that of Jupiter, nay, he that hath not
very good eyes, will very hardly diſcern it; from whence it may
be rationally inferred, that the ſaid ſtar, as having a much more
lively light than Jupiter, maketh its irradiation greater than
ter doth his. In the next place, as to the irradiation of the Sun
and Moon, it is as nothing, by means of their magnitude, which
poſſeſſeth of it ſelf alone ſo great a ſpace in our eye, that it
veth no place for the adventitious rayes; ſo that their faces ſeem
cloſe clipt, and terminate. We may aſſure our ſelves of the ſame
truth by another experiment which I have often made triall of;
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