Scripta clarissimi mathematici M. Ioannis Regiomontani, de torqueto, astrolabio armillari, regula magna ptolemaica, baculo[que] astronomico, & observationibus cometarum, aucta necessariis, Ioannis Schoneri ... additionibus. Item observationes motuum solis, ac stellarum tam fixarum [qua ...] erraticarum. Item libellus M. Georgii Purbachii de quadrato geometrico ...

when the Sun has already sunk below the horizon and the stars are beginning to shine, express the configuration of the sky through the place of the Moon previously found, as was explained in the third problem. Consider how much of an arc from the equinoctial circuit the place of the Sun has traveled in the interval between the two observations, so that you may know the mean time by taking four minutes of one hour for each degree, and again, for each equal hour, add nearly half a degree, and for the remaining minutes, if there are any, add a proportional part to the place of the Moon elicited through the first observation, so that the place of the Moon at the hour of the second observation is held approximately. Place the ruler of longitude over this, and express the configuration of the sky as we advised before. With the region of the signs fixed, move the crest hither and thither until the star is seen directly from the circle of latitude and at the same time through both holes of its ruler. For then each ruler will perform its office as far as can be done; for the ability to arrive at the inner truth by this way is not given, since the foundation of the matter is fluid and fragile. For in the first observation, the true place of the Moon is not detected, as the diversity of aspect parallax prohibits it; nor in the second, due both to the diversity of aspect and to the inequality of the lunar motion, which in an equal hour extends now short of and now beyond half a degree.

SIXTH PROBLEM.

To detect the elevation of the Sun or of any other star above the horizon.

Set the instrument as explained above, and with the ruler of longitude placed at the place of the Sun in the ecliptic signifer, and kept there so that it does not slide anywhere, turn the region of the signs hither and thither until the solar ray, falling onto the hole of the front sight, penetrates to the hole of the rear sight. For soon the thread of the plumb line, hanging from the suspended semicircle, will indicate the degrees of elevation