Archimedes Texts

291
ed; therefore tell me how he dis-ingageth himself in the next place
from that particular of the Stars having constantly kept the same
distance from the fixed Stars circumjacent to it.

SALV. He betakes himself, in like manner, to two threads, yet
more unable to uphold him than the former: one of which is like
wise fastened to refraction, but so much less firmly, in that he
saith, that refraction operating upon the new Star, and sublimating
it higher than its true situation, maketh the seeming distances un
tain to be distinguished from the true, when compared to the cir
cumposed fixed Stars that environ it. Nor can I sufficiently ad
mire how he can dissemble his knowing how that the same refra
ction will work alike upon the new Star, as upon the antient one
its neighbour, elevating both equally, so as that such a like acci
dent altereth not the space betwixt them. His other subterfuge is
yet more unhappy, and carryeth with it much of ridiculous, it be
ing founded upon the errour that may arise in the instrumen talo
peration it self; whilst that the Observator not being able to
constitute the centre of the eyes pupil in the centre of the Sex
tant (an Instrument imployed in observing the distance between
two Stars) but holding it elevated above that centre, as much as
the said pupil is distant from I know not what bone of the cheek,
against which the end of the Instrument resteth, there is formed
in the eye an angle more acute than that which is made by the sides
of the Instrument; which angle of rayes differeth also from it
self, at such time as a man looketh upon Stars, not much elevated
above the Horizon, and the same being afterwards placed at a
great height; that angle, saith he, is made different, while the In
strument goeth ascending, the head standing still: but if in moun
ting the Instrument, the neck should bend backwards, and the
head go rising, together with the Instrument, the angle would then
continue the same. So that the Authours answer supposeth that
the Observators in using the Instrument have not raised the head,
as they ought to have done; a thing which hath nothing of likeli
hood in it. But granting that so it had been, I leave you to judge
what difference can be between two acute angles of two equicru
ral triangles, the sides of one of which triangles are each four
[Italian] Braces [i.e. about three English yards] and those of the
other, four braces within the quantity of the diameter of a Pea;
for the differences cannot be absolutely greater between the length
of the two visive rayes, whilst the line is drawn perpendicularly
from the centre of the pupil, upon the plain of the Rule of the
Sextant (which line is no bigger than the breath of the thumb)
and the length of the same rayes, whilst elevating the Sextant,
without raising the head together with it, that same line no longer
falleth perpendicularly upon the said plane, but inclineth, making