Encyclopaedia; or, A dictionary of arts, sciences, and miscellaneous literature; constructed on a plan, by which the different sciences and arts are digested into the form of distinct treatises of . , the focal diilance of the parallel rays for tlieconcave lens is one halt, and for the convex glafs one-third ot the combined focus. When put together,they refrait the rays in the following manner. Letab, ab (fig. 4.), be two red rays of the funs lightfalling parallel on the firft convex lens c. Suppofmgthere was no other lenj jyd^Bt, but that one, theywould then be converged^^lnto the l
Encyclopaedia; or, A dictionary of arts, sciences, and miscellaneous literature; constructed on a plan, by which the different sciences and arts are digested into the form of distinct treatises of . , the focal diilance of the parallel rays for tlieconcave lens is one halt, and for the convex glafs one-third ot the combined focus. When put together,they refrait the rays in the following manner. Letab, ab (fig. 4.), be two red rays of the funs lightfalling parallel on the firft convex lens c. Suppofmgthere was no other lenj jyd^Bt, but that one, theywould then be converged^^lnto the lines be be, and atlaft meet in the focus y. Let the lines gb, gh, two violet rays falling oti the furface of thelens. Thefe are alfo refracted, ana will meet in a fo-cus ; bat as they have a greater degree of refrangibi-lity than the red rayS, they of confequence con-verge more by the fame power of refraflion intheglals, and meet fooner in a focus, fupjjofe at r.—Letnow the concave lens dd be plaeed in fuch a manneras to intercept all the rays before they come to theirfociis. Were this lens made of the fame materials, andground to the fame radius with the convex one, it would OPllVS. ^//tae^arti Part I. Iclcfcopc. OPT would have the fame power to caufe the rays divergetiuit the f rmcr liad to nudve them converge. In tliiscafe, the red rays would become parallel, and move on I s. in the Hue o o. But the concave lens bciuc; made IUte Cjclxv. of Flint , and upon a ihoi ter radius, has a greaterrcfraclive power, and therefore they diverge a littleafter they ccme out of it; and it no third lens wasinterpofed, they would proceed diverging in the lines0 p I, opt; but, by the intci-pofition of the third lens0 II0, they are again made to converge, and meet in afocus fomewhat more diftant than the former, as at . the concave lens the violet rays are alfo refrafled,and made to diverge : but having a greater degree ofrcfrangibility, the fame power of refraction
Size: 1468px × 1702px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1700, bookdecade1790, bookidencyclopaedi, bookyear1798
