Salusbury, Thomas, Mathematical collections and translations (Tome I), 1667

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1ſtanding of which, I ought firſt to advertiſe you, that when ever
the
new Star, or other Phænomenon is near to the earth, turning
with
a Diurnal motion about the Pole, it will ſeem to be farther
off
from the ſaid Pole, whilſt it is in the lower part of the
an
, then whilſt it is above, as in this Figure [being fig. third of
this
Dial.] may be ſeen.
In which the point T. denotes the
tre
of the Earth; O the place of the Obſervator; the Arch VPC
the
Firmament; P. the Pole.
The Phænomenon, [or appearance]
moving
along the Circle F S. is ſeen one while under the Pole by
the
Ray O F C. and another while above, according to the Ray
O
S D. ſo that the places ſeen in the Firmament are D. and C. but
the
true places in reſpect of the Centre T, are B, and A,
ſtant
from the Pole.
Where it is manifeſt that the apparent place
of
the Phænomenon S, that is the point D, is nearer to the Pole than
the
other apparent place C, ſeen along the Line or Ray O F C,
which
is the firſt thing to be noted.
In the ſecond place you muſt
note
that the exces of the apparent inferiour diſtance from the Pole,
over
and above the apparent ſuperiour diſtance from the ſaid Pole,
is
greater than the Inferiour Parallax of the Phænomenon, that is, I
ſay
, that the exceſſe of the Arch C P, (the apparent inferior
ſtance
) over and above the Arch P D, (the apparent ſuperior
ſtance
) is greater then the Arch C A, (that is the inferiour
lax
.) Which is eaſily proved; for the Arch C P. more exceedeth
P
D, then P B; P B, being bigger than P D, but P B. is equal to
P
A, and the exceſſe of C P, above P A, is the arch, C A,
fore
the exceſſe of the arch C P above the arch P D, is
er
than the arch C A, which is the parallax of the Phænomenon
placed
in F, which was to be demonſtrated.
And to give all
vantages
to the Author, let us ſuppoſe that the parallax of the ſtar
in
F, is the whole exceſſe of the arch C P (that is of the inferiour
diſtance
from the pole) above the arch P D (the inferiour
ſtance
.) I proceed in the next place to examine that which the
obſervations
of all Aſtronomers cited by the Authour giveth us,
amongſt
which, there is not one that maketh not againſt himſelf
and
his purpoſe.
And let us begin with theſe of Buſchius, who
findeth
the ſtars diſtance from the pole, when it was ſuperiour, to be
28
gr. 10 m. and the inferiour to be 28 gr. 30 m. ſo that the
ceſſe
is 0 gr. 20 m. which let us take (in favour of the Author) as
if
it all were the parallax of the ſtar in F, that is the angle T F O.
Then the diſtance from the Vertex [or Zenith] that is the arch
C
V, is 67 gr. 20 m. Theſe two things being found, prolong the
line
C O, and from it let fall the perpendicular T I, and let us
conſider
the triangle T O I, of which the angle I is right angle,
and
the angle I O T known, as being vertical to the angle V O C,
the
diſtance of the ſtar from the Vertex, Moreover in the triangle

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