PHYSICAL AND MATHEMATICAL SCIENCES. 12“

instead of Roman capitals, which had hitherto beenemployed; thus bringing the notation almost exactlyinto its present form. His labours were encouraged,and even a maintenance afforded him by that liberalpatron of science and letters, Henry Percy, earl of Nor-thumberland.*

Progress of Optics, Mechanics, &jc.

Maurolycus , already mentioned as a mathematician,was also distinguished in optics. He conceived theuse of the crystalline lens in the eye, though not theoffice of the retina; and the application of lenses forremedying both long and short sight. In his work,“ Theoremata de Lumine et Umbra” (1575), he givesan explanation of the fact noticed by Aristotle , that thelight of the sun passing through a small hole of what-ever shape, always gives a circular illuminated space ona screen at a little distance. The rays from the differentparts of the sun’s disk cross at the aperture (which wewill suppose to be, for example, triangular), and eachray gives a small triangular bright spot on the screen ;these being partially superposed, hut arranged in theform of the sun’s disk, will give an image sensibly cir-cular ; and the more accurately so as the hole is smaller,or the screen more distant.

This principle is precisely that of the camera ob-scura in its simplest form, which was invented aboutthis time (1560) by Baptista Porta , who described it ina work entitled “ Magia Naturalis.” The subsequentaddition of a lens at the aperture, only substitutes theartificial crossing of the rays at the centre of the lens,and at the same time increases the quantity of light.He perceived, in general, the resemblance between thisconstruction and that of the eye ; hut extraordinary asit may seem, failed in tracing the place of the image,

* Some highly interesting particulars of his analytical labours will befound in Prof. Rigaud’s “Supplement to the Works of Bradley.” Oxf.18:33, pp. 43. 52, &c. To his astronomical pursuits we shall refer in anotherplace.