It's from Nicolaus Copernicus' "De revolutionibus orbium coelestium" (Generally translated into English as "On the Revolutions of the Heavenly Spheres") first printed in 1543 and consisting of six books. The part that you posted is from Book II.

You can actually access that book in a printed script (which should be more legible than the cursive version you posted) from the website of the Harvard University HERE .

For the start of the part you posted, click on "Second Book (Liber Secundus)" and scroll down to page 4 of that PDF and search the bottom of that page for "circulum meridianum".