Archimedes Texts

SALV. I will use my utmost endeavours to render my self

intelligible, but the difficulty of the accident it self, and the
great attention of mind requisite for the comprehending of it,
constrains me to be obscure. The unequalities of the additions
and substractions, that the diurnal motion maketh to or from
the annual dependeth upon the inclination of the Axis of the di
urnal motion upon the plane of the Grand Orb, or, if you please,
of the Ecliptick; by means of which inclination the Equinoctial
intersecteth the said Ecliptick, remaining inclined and oblique
upon the same according to the said inclination of Axis. And the
quantity of the additions importeth as much as the whole diame
ter of the said Equinoctial, the Earths centre being at the same
time in the Solstitial points; but being out of them it importeth
lesse and lesse, according as the said centre successively approa
cheth to the points of the Equinoxes, where those additions are
lesser than in any other places. This is the whole businesse, but
wrapt up in the obscurity that you see.

The causes of
the inequality of
the additions and
substractions of the
diurnal conversion
from the annual
motion.

SAGR. Rather in that which I do no not see; for hitherto I
comprehend nothing at all.

SALV. I have already foretold it. Neverthelesse we will try
whether by drawing a Diagram thereof, we can give some
small light to the same; though indeed it might better be set
forth by solid bodies than by bare Schemes; yet we will help our
selves with Perspective and fore-shortning. Let us draw there
fore, as before, the circumference of the Grand Orb, [as in
Fig. 4.] in which the point A is understood to be one of the
Solstitials, and the diameter A P the common Section of the
Solstitial Colure, and of the plane of the Grand Orb or Eclip
tick; and in that same point A let us suppose the centre of the
Terrestrial Globe to be placed, the Axis of which C A B, in
clined upon the Plane of the Grand Orb, falleth on the plane of
the said Colure that passeth thorow both the Axis of the Equino
ctial, and of the Ecliptick. And for to prevent confusion, let
us only draw the Equinoctial circle, marking it with these chara
cters D G E F, the common section of which, with the plane of
the grand Orb, let be the line D E, so that half of the said E
quinoctial D F E will remain inclined below the plane of the
Grand Orb, and the other half D G E elevated above. Let
now the Revolution of the said Equinoctial be made, according
to the order of the points D G E F, and the motion of the cen
tre from A towards E. And because the centre of the Earth
being in A, the Axis C B (which is erect upon the diameter of
the Equinoctial D E) falleth, as hath been said, in the Solsti
tial Colure, the common Section of which and of the
Grand Orb, is the diameter P A, the said line P A shall