Salusbury, Thomas, Mathematical collections and translations (Tome I), 1667
page |< < of 701 > >|
1[as in Fig. 5.] and the Axis, as before A C, by which the plane
of our Meridian would paſſe, in which plane ſhould alſo be the
Axis of the Suns revolution, with its Poles, one towards us, that
is, in the apparent Hemiſphere, which Pole we will repreſent by
the point E, and the other ſhall fall in the occult Hemiſphere,
and I mark it I.
Inclining therefore the Axis E I, with the
riour part E, towards us, the great circle deſcribed by the Suns
converſion, ſhall be this B F D G, whoſe half by us ſeen,
ly B F D, ſhall no longer ſeem unto us a right line, by reaſon the
Poles E I are not in the circumference A B C D, but ſhall appear
incurvated, and with its convexity towards the inferiour part C.
And it is manifeſt, that the ſame will appear in all the leſſer
cles parallel to the ſame B F D.
It is to be underſtood alſo, that
when the Earth ſhall be diametrically oppoſite to this ſtate, ſo
that it ſeeth the other Hemiſphere of the Sun, which now is hid,
it ſhall of the ſaid great circle behold the part D G B incurved,
with its convexity towards the ſuperiour part A; and the
ſes of the ſpots in theſe conſtitutions ſhall be firſt, by the arch
B F D, and afterwards by the other D G B, and the firſt
tions and ultimate occultations made about the points B and D,
ſhall be equilibrated, and not thoſe that are more or leſſe
ted than theſe.
But if we conſtitute the Earth in ſuch a place
of the Ecliptick, that neither the boundary A B C D, nor the
Meridian A C, paſſeth by the Poles of the Axis E I, as I will ſhew
you anon, drawing this other Figure [viz. Fig. 6.] wherein the
apparent or viſible Pole E falleth between the arch of the
nator A B, and the ſection of the Meridian A C; the diameter
of the great circle ſhall be F O G, and the apparent ſemicircle
F N G, and the occult ſemicircle G S F, the one incurvated with
its convexity N towards the inferiour part, and the other alſo
bending with its convexity S towards the upper part of the Sun.
The ingreſſions and exitions of the ſpots, that is, the termes F
and G ſhall not be librated, as the two others B and D; but F
ſhall be lower, and G higher: but yet with leſſer difference
than in the firſt Figure.
The arch alſo F N G ſhall be
ted, but not ſo much as the precedent B F D; ſo that in this
ſition the paſſages or motions of the ſpots ſhall be aſcendent
from the left ſide F, towards the right G, and ſhall be made by
curved lines.
And imagining the Earth to be conſtituted in the
poſition diametrically oppoſite; ſo that the Hemiſphere of the
Sun, which was before the occult, may be the apparent, and
minated by the ſame boundary A B C D, it will be manifeſtly
diſcerned, that the courſe of the ſpots ſhall be by the arch G S F,
beginning from the upper point G, which ſhall then be likewiſe
from the left hand of the beholder, and going to determine,

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