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 . le. They are moft viliblewhen the eyes are turned towards an uniform whiteobjecl, as the fllov^ in the open field. If they befixed the eye is fo, this philofopher fuppofedthat they were occafioned by extravaf4ted blood uponthe retina. But he that the moveable fpotswere occafioned by opaque matter floating in theaqueous humour of .he eye. He thought the vitreoushumour was
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 . le. They are moft viliblewhen the eyes are turned towards an uniform whiteobjecl, as the fllov^ in the open field. If they befixed the eye is fo, this philofopher fuppofedthat they were occafioned by extravaf4ted blood uponthe retina. But he that the moveable fpotswere occafioned by opaque matter floating in theaqueous humour of .he eye. He thought the vitreoushumour was notfufficientlylimpid forthis pnrpofe. By the follownig calculation, M. de la Hire givesus an idea of the extreme fenfibility of the optic may fee very eafily, at the diilance of 4000 tiifes,the fail of a , 6 feet in diameter; and theeye being fuppofed to be an inch in diameter, the piiSureof this fail, at tne bottom of the eye, will be -^ttc-s- ofan inch, which is lefs than the C66th part ot aline, andis about the 66th part of a common hair, or the 8thpart of a fingle thread of fvlk. So fmall, therefore,muft one of the fibres of the optic nerve be, whicli he favs Plate CCCLX J/.. 7/i/t^-tr Part II. O 329 .?^Pliardtit Tjys is almoft Inconceivable, fince each of thefe fibres objeft, as. a candle, tliere will be fccn two ima^cs. Apparentr^ ^<^- is a tube that contains fpirits. If birds perceive di- one ereifl, and tlie other inverted. The firft is made ?»< &>:.lit oiij^cds. Q,j|^^ objefts as well as men, which he thinks very fimply by refleaion from the ncared furface, the ^ oJg3-probable, he obfcrves that the fibres of their optic fecond by refleiftion from the farther furface, the rays ^ J, nerves mull be much finer than ours. undergoing a refraflion frim the firft furface both be- Eerk. leys i^he pcrfon who firft took much notice of Dr Bar- fore and after the rcficLlion. If this p^lafs has not tooaccnnnt of rows hypotliefis was the ingenious Dr
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Keywords: ., bookcentury1700, bookdecade1790, bookidencyclopaedi, bookyear1798
