Question

Does anyone know anything about the mathematical jewel. and what it does? 50 points​

Answer 1

I think The Mathematical Jewel (1585) was his most popular and influential publication. The “Jewel” of the title was an astrolabe designed by Blagrave and considered superior for its time. The title page (shown above) proclaims the book’s contents:

The mathematical ievvel, shewing the making, and most excellent vse of a singuler instrument so called: in that it performeth with wonderfull dexteritie, whatsoeuer is to be done, either by quadrant, ship, circle, cylinder, ring, dyall, horoscope, astrolabe, sphere, globe, or any such like heretofore deuised: ...