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 . r firft and fecond focufes V andG will defcnbe ciscuhir arches VT and GF whofecentres are R and E. For the line RV is invariable;being in proportion to RB in a given ratio of the lef-fer of the fines of incidence and refraction to their dif-ference* ; confequcntly tlie line EG is alfo invariable,being in proportion to the given line RV in the givenratio of rE to rR, bccaufe the triangles
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 . r firft and fecond focufes V andG will defcnbe ciscuhir arches VT and GF whofecentres are R and E. For the line RV is invariable;being in proportion to RB in a given ratio of the lef-fer of the fines of incidence and refraction to their dif-ference* ; confequcntly tlie line EG is alfo invariable,being in proportion to the given line RV in the givenratio of rE to rR, bccaufe the triangles EGr, RVr areequiargular. Co-ol. 2. The laft proportion gives the followingrule for finding the focal diilance of any thin lens. AsRr, the interval between the centres of the furfaces,is to rE, the femidiameter of the fecond futface, fo isRV or RT, the continuation of the firft femidiameterto the firft focus, to EG or EF, the focal oiftance ofthe lens; which, according as the l;ns isthicker orthinner in the middle than at its edges, muft lie oa the Part I. Of 7. to 143Tilt focusof parallelrays fallingpernendi-calarlyupon anylens. ? Corel,from Lemnia. * By a for-mcr Prop. Flatc CCCL\.. Jifetc^arf^ i :K. Plate CCCIAl
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Keywords: ., bookcentury1700, bookdecade1790, bookidencyclopaedi, bookyear1798
