SEE 



SEE 



Mark, on the river Aland, which almoft furrounds it ; 

 40 miles N.W. of Brandenburg. N. lat. 52° 53'. E. long. 

 11° 59'. — Alfo, a town of the duchy of Bremen ; 3 miles 

 W. of Bremen. — Alfo, a town of Weitphalia, called 

 " Sommerchenburg," in the duchy of Magdeburg ; 1 8 miles 

 W. of Macjdeburg. 



SEEHAUSZ, a citadel of Germany, in the lordfhip of 

 Schwarzeuherg, on a lake ; 6 miles S. of Scheinfeld. 



SEE-HOO, or 3l-H0U, a lake of China, on the borders 

 of which (lands the wealthy and extenfive city of Hang- 

 choo-foo, or Hang-tcheou-fou ; which fee. This lake, with 

 the furrounding fcenery, is accounted one of the grandeft, 

 as well as moft beautiful, fpots in all China. The Lui- 

 fang-ta, or tower of the thundering winds, (landing on the 

 point of a promontory, jutting into the lake, forms a bold 

 objedl. It is faid to have been built in the time of the phi- 

 lofopher Confueius, who lived centuries before the Chrif- 

 tian era. The vale of tombs has an almoll infinite variety 

 of ornaments. Naked coffins in great abundance lie fcat- 

 tered upon the ground, and the fides of the hills that rife 

 from the vale are thickly fet with groups of larcophagi, 

 in the fhape of fmall houfes, arranged in fuch a manner as 

 to have the appearance of fo many LiUiputian cottages. In 

 the plates annexed to Staunton's Voyage, we have an in- 

 tereding view of this lake. 



SEEHURAH, a town of Hindooftan, in (Jurry-Mun- 

 della ; 25 miles N. of Gurrah. 



SEEING, the aft of perceiving objefts by the organ of 

 fight ; or, it is the fenfe we have of external objefts, by 

 means of the eye. 



For the apparatus, or difpofition of the parts necedary 

 to feeing, fee Eye. For the manner in which feeing is 

 performed, and the laws of it, fee Vision. 



Our bed anatomids differ greatly as to the caufe why we 

 do not fee double with the two eyes. Galen, and others 

 after him, afcribe it to a coalition, or deculTation of the 

 optic nerve, behind the os fphenoides. But whether they 

 decuffate or coalefce, or only barely touch one another, is 

 not fo well agreed. 



The Bartholines and Vefalius fay exprefsly, they are 

 united by a perfeft confufion of their fubllance ; Dr. Gib- 

 Ion allows them to be united by the clofell conjunftion, but 

 not by a confufion of their fibres. 



Alhazen, an Arabian philofopher of the 12th century, 

 accounts for fingle vifion by two eyes, by fuppofing that 

 when two corrcfponding parts of the retina are affefted, the 

 mind perceives but one image. 



Defcartes, and others, account for the elfeft another way ; 

 viz. by fuppofing that the fibrillae conftituting the medullary 

 part of thofe nerves, being fpread in the retina of each eye, 

 have each of them correfponding parts in the brain ; fo that 

 when any of thofe fibrillae are ilruck by any parts of any 

 image, the correfponding parts of the brain are affefted 

 thereby. 



Somewhat like which is the opinion of Dr. Briggs, who 

 takes the optic nerves of each eye to confill of homologous 

 fibres havmg their rife in the thalamus nervorum opti- 

 corum, and being thence continued to both the retinas, 

 which are compofed of them ; and farther, that thofe 

 fibrillK have the fame parallehfm, tenfion, &c. in both eyes ; 

 confequently, when an image is painted on the fame cor- 

 refponding fympathizing parts of each retina, the fame 

 effefts are produced, the fame notice carried to the thalamus, 

 and fo imparted to the foul. Hence is that double vifion en- 

 fuing upon an interruption of the parallellifm of the eyes ; 

 as when one eye is deprefled by the finger, or their fym- 

 phony is interrupted by difeafe : but Dr. Briggs maintains, 



that it is but in few fubjefts there is any dccullation ; and in 

 none any conjunftion more than merecontaft. 



Dr. Briggs's notion is by no means confonant to fafts, and 

 is attended with many improbable circumltances. 



It was the opinion of fir Ifaac Newton, and of many 

 others, that objefts appear fingle, becaufe the two optic 

 nerves unite before they reach the brain. But Dr. Porter- 

 field (hews, from the obfervation of feveral anatomifts, that 

 the optic nerves do not mix, or confound their fubftance, 

 being only united by a clofe cohefion ; and objefts have ap- 

 peared fingle, where the optic nerves were found to be dif- 

 joined. To account for this phenomenon, this ingenious 

 writer fuppofes, that, by an original law in our natures, we 

 imagine an objeft to be fitualed foraewhere in a riglit line 

 drawn from the pifture of it upon the retina, through tiic 

 centre of the pupil ; confequently the fame objeft appearing 

 to both eyes to be in the fame place, the mind cannot diltin- 

 gui(h it into two. 



In anfwer to an objeftion to this hypotheCs, from objefts 

 appearing double when one eye i? diftorted, he fays, the 

 mind miilakes the pofition of the eye, imagining, that it 

 had moved in a manner correfpondmg to the other, in which 

 cafe the conclufion would have been jull : in this he fcems 

 to have recourfc to the power of habit, though he difclaims 

 that hypothefis. This principle, however, has b^en thought 

 fufficient to account for this appearance. 



Originally, every objeft making two piftures, one in each 

 eye is imagined to be double ; but, by degrees, we find that 

 when two correfponding parts of the retina are imprcffed, 

 the objeft is but one ; but if thofe correfponding parts be 

 changed by the diftortion of one of the eyes, the objeft muft 

 again appear double, as at the firlt. This feems to be verified 

 by Mr. Chefclden, who informs us, that a gentleman, who. 

 from a blow on his head, had one eye dillorted, found every 

 objeft to appear double, but by degrees the mod familiar 

 ones came to appear fingle again, and in time all objefts did 

 fo without amendment of the dillortion. A fimilar cafe is 

 mentioned by Dr. Smith. 



On the other hand Dr. Reid is of opinion, that the cor- 

 refpondence of the centres of two eyes, on which fingk 

 vifion depends, does not arife from cudom, but from fome 

 natural conditution of the eye and of the mind. 



M. du Tour adopts an opinion, long before fuggedcd by 

 GafTendi, that the mind attends to no more than the image 

 made in one eye at a time ; in fupport of which he produces 

 feveral curious experiments; but as M. Buffon oblcrves, it 

 is a fufficient anfwer to this hypothefis, that we fee more dif- 

 tinftly with two eyes than with one ; and that when a round 

 objeft is near us, we plainly fee more ot the furface in one 

 cafe than in the other. 



With relpeft to fingle vifion with two eyes. Dr. Hartley 

 obferves, that it deferves particular attention, that the optic 

 nerves of men, and fuch other animals as look the fame way 

 with both eyes, unite in the fella turcica in a ganglion, or 

 little brain, as it may be called, peculiar to themfelves, and 

 that the adociations between fynchronous impredions on the 

 two retinas mud be made fooner, and cemented dronger on 

 this account ; and that they ought to have a much greater 

 power over one another's images than in any other part of 

 the body. And thus an imprelfion made on the right eye 

 alone by a fingle objeft, may propagate itfelf into the left, 

 and there raiie up an image almoil equal in vividnefs to 

 itfelf; and, confequently, when v/n fee whh one eye only, 

 we may, however, have piftures in both eyes. 



It is a common obfervation, fays Dr. Smith, that objefts 

 feen with both eyes appear more vivid and dronger than they 

 do to a fingle eye, efpecially when both of them are equally 



good. 



