Galilei, Galileo Dialogues on two world systems 1661, tr. Salusbury, Thomas

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answer that sufficeth to satissie at once the course of the spots,
and the discourse of the Mind. I will explain unto you so much
as I remember thereof, that so you may judge thereon as seems
best unto you.

The Pure Peri­
patetick Philoso­
phers will laugh at
the spots and their
Phænomena, as
illusions of the
Chrystals in the
Telescope.

Supposing that the apparent motions of the Solar spots are the
same with those that have been above declared, and supposing the
Earth to be immoveable in the centre of the Ecliptick, in whose
circumference let the center of the Sun be placed; it is necessary
that of all the differences that are seen in those motions, the cau­
ses do reside in the motions that are in the body of the Sun:
Which in the first place must necessarily revolve in it self (i. e.

about its own axis) carrying the spots along therewith; which
spots have been supposed, yea and proved to adhere to the So­
lar superficies. It must secondly be confest, that the Axis of the
Solar conversion is not parallel to the Axis of the Ecliptick, that
is as much as to say, that it is not perpendicularly erected upon
the Plane of the Ecliptick, because if it were so, the courses and
exitions of those spots would seem to be made by right lines pa­
rallel to the Ecliptick. The said Axis therefore is inclining, in
regard the said courses are for the most part made by curve lines.
It will be necessary in the third place to grant that the inclinati­
on of this Axis is not fixed, and continually extended towards
one and the same point of the Universe, but rather that it doth
alwayes from moment to moment go changing its direction; for
if the pendency should always look towards the self same point,
the courses of the spots would never change appearance; but
appearing at one time either right or curved, bending upwards
or downwards, ascending or descending, they would appear
the same at all times. It is therefore necessary to say, that the
said Axis is convertible; and is sometimes found to be in the
Plane of the circle that is extreme, terminate, or of the visible
Hemisphere, I mean at such time as the courses of the spots
seem to be made in right lines, and more than ever pendent,
which happeneth twice a year; and at other times found to be in
the Plane of the Meridian of the Observator, in such sort that
one of its Poles falleth in the visible Hemisphere of the Sun, and
the other in the occult; and both of them remote from the ex­
treme points, or we may say, from the poles of another Axis of
the Sun, which is parallel to the Axis of the Ecliptick; (which
second Axis must necessarily be assigned to the Solar Globe) re­
mote, I say, as far as the inclination of the Axis of the revolution
of the spots doth import; and moreover that the Pole falling in
the apparent Hemisphere, is one while in the superiour, another
while in the inferiour part thereof; for that it must be so, the
courses themselves do manifestly evince at such time as they are