Quomodo Solis eclipsis videri possit,
Nunc apponere decreui modum, quo Solis eclipsis clare
notari possit. In Solis eclipsi claude cubiculi fenestras atque
oppones foramini papyrum, et videbis Solem, Speculo
concavoin oppositam papyrum resiliat, et circulum suae
rotunditatis describas, sic initio, medio, et sinefaces. Unde
sene visus laesione diametri puncta Solis defectus notabis.
How the eclipse can be seen,
Now I have decided to set the manner in which an eclipse clearly can be observed. In the eclipse room, shut the windows and opposite the paper opening, and you will see the Sun, the concave mirror bouncing back to the opening in the paper, and his circle defines the round shape, at the beginning, during the middle, and at the end. Thus, while progressing observing a lesion in diametric points of the Sun you will notice the defect.
(Translated with the help of Google Translate. It's probably in need of a little more refinement.)