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: ...
If wavelengths of light
from a definite region of the spectrum are engrossed by a material, then the
materials will appear to be the complementary color. If violet light with
wavelength of 400nm is immersed, the material will look yellow. If the material
engrosses blue you will perceive the color orange.
