SEE 



Vol. XXXII. 



SCOTLAND, col. 22, 1. 29, for extent r. extind. 



SCOTS, 1. 2, infcrt — thofe of the town included. 



SCREEN, Skheen, or Altak-skreen, in Archilec- 

 lure. (See Reredos.) The choir-fcreen is the fence 

 which fenarates the choir from the nave of the church. 



SCRIVAN. Add — of whom 1816 were flaves in 



SCROFULOUS.orScnopiiuLou.s Tumowrj. See Scro- 

 niui.A, Uu'-JOJST, Di/eafi of. White-swelling, &c. 



SCRUBGRASS, in Geography, a townfhip of Venango 

 county, in Pennfylvania, containing 540 inhabitants. 



SCULPTURE, co!. 2, 1. 22, omit the colon after 

 required, and infert a comma after manner. 



SEABROOK, 1. 2, r. 774. 



SEAL. Add — The broad feal of England was ftolen 

 from the lord chancellor's houfe in Ormond-ftreet, March 

 24th, 1784; and a new one was brought into ufe, upon 

 the union of Ireland with Great Britain, January ift, 1801. 



Seal, in Geography, a townfhip of Scioto county, in 

 Ohio, having 379 inhabitants. 



SEBASTICOOK, a townfhip of America, in the dif- 

 trift of Maine, and county of Somerfet, having 105 per- 

 fons. 



SECRETIONS, Secreted F/u':Js, Chemical Properties 

 of. See Fluids, Animal. 



SECTS of Hindoos, col. 2, 1. 8 and 23 from bot- 

 tom for Bhon r. Bhow. Col. 10, 1. 31, tranfpofe the 

 points. 



SEDATIVUM Sal. Add after Salt— under the 

 article Salts. 



SEEING, col. 3, 1.5, add- Dr. Wells, in his " EITay 

 on fingle Vifion with two Eyes," has reduced the principal 

 opinions upon this fubjeft into two clades. The firft clafs 

 comprehends thofe of Galen, Alhazcn, Rohault, Dr. Briggs, 

 and fir Ifaac Newton ; all of whom have regarded the 

 queftion as equivalent to the following one : Why (hould 

 the mind be affcftcd with only one perception from two 

 imprcfTions upon the external organs of fight, fince either of 

 thofe imprcfTions is of itfelf fufficient to produce a fimilar 

 perception ? To this queftion they reply, that the two 

 impreflions are united before they are communicated to the 

 mind, and they only differ concerning the manner in which 

 fuch an union takes place. Againll the opinions now ftated 

 Dr. Wells objcfts, that they muft be confidered as mere 

 conjeftures, founded upon certain fuppofed changes in the 

 brain and nerves, the exiftence of which, from the nature 

 of the parts, it is impoflible either to demonftrate or to 

 refute by experiments ; and that no one of them, though 

 admitted to be true, is yet fufficient to explain the pheno- 

 mena on account of which it was framed. To the fecond 

 clafs. Dr. Wells refers the opinions of thofe who maintain, 

 that an objcft is feen fingle by both eyes, becaufe it is feen 

 by each of them in the fame external place ; and who pro- 

 fefs to point out fome law, or conftant rule of vifion, from 

 , which this famenefs of place, is to be derived as a neceflary 

 confequence. This view of the queftion, as our author 

 imagines, was firft fuggefted by Aguilonius, and it has 

 been fince adopted by Dechales, Dr. Porterfield, Dr. Smith 

 of Cambridge, and Dr. Reid of Glafgow. 



Aguilonius, who has been followed in the fame train of 

 reafoning by Dechales and Dr. Porterfield, begins with 

 defining the terms horopter and plane of the horopter. If a 



SEE 



line be drawn through the point of the mutual interfeftion 

 of the optic axes, parallel to the interval between the eyes, 

 this from its office is denominated the horopter ; and a 

 plane, fuppofed to pafs through this fine perpendicular to 

 the plane of the optic axes, is called by Aguilonius the 

 plane of the horopter. According to his ftatement, it is a 

 law of our conftitution, that all bodies which we fee with, 

 one glance or look, whatever are their real places, appear 

 to each eye to be fituated in this plane ; and upon this 

 fuppofition he (hews why fome fhould be feen fingle with 

 two eyes, and others double. For according to a recent 

 opinion, which he has advanced, and which other writers on 

 vifion have not contradicted, the two lines of dircftion in 

 which an objeft is feen with both eyes, can meet each other 

 only in one point, and therefore all bodies which are really 

 fituated in the plane of the horopter, muft neceffarily appear 

 fingle, as the lines of direftion in which any one of them 

 is perceived by the two eyes, coincide in that plane, and 

 no where elfe ; and all bodies which are not fituated in the 

 plane of the horopter muft as neceffarily appear double, 

 fince, in this cafe, the lines of their vifible direftions inter- 

 feft each other, either before or after they pafs through it. 

 To this reafoning Dr. Wells replies, that if the vifible 

 places of all bodies were contained in the plane of the 

 horopter, they would appear of magnitudes proportional to 

 the angles which they lubtended at the eye ; e. gr. a finger 

 held near to the face would feem as large as the part of a 

 remote building which it might conceal from the fight. 

 But this is contrary to experience, and therefore no rea- 

 foning that depends upon it can be admitted. 



If it be allied, fays Dr. Smith, why, in feeing with 

 both eyes, we do not always fee double, becaufe of a 

 double fenfation, it is fufficient to reply, that in the ordi- 

 nary ufe of our eyes, in which the pictures of an objeft are 

 conftantly painted upon " correfponding places or points" 

 of the retinas, the predominant ienfe of feeling has origin- 

 ally and conftantly informed us that the objedl is fingle. 

 What he means by " correfponding points," he thus ex- 

 plains : When the optic axes are parallel, or meet in a 

 point, the two middle points of the retinas, or any points 

 which are equally diftant from them, and lie on the fame 

 fides of them, either towards the right hand or left hand, 

 or upwards or downwards, or in any oblique direttion, are 

 called " correfponding points." Accordingly our idea of 

 the outward place of an objeA is connected with both 

 thefe fenfations ; as is manifeft by its appearing in two 

 places when its pifkures are not painted upon correfpond- 

 ing places of the retinas ; which is only a diredt confe- 

 quence arifing from our general habit of feeing. If it be 

 aflced why, in order to produce fingle vifion, all men agree 

 in directing their eyes toward the objecft in fuch a manner as 

 to receive its piftures upon correfponding pointsof the retinas, 

 fince cuftom might have connected the fenfations of any other 

 two points with the information of its unity from feehng ? 

 To this objection, fuggefted by Dr. Reid, the reply may 

 be made in Dr. Smith's own words (vol. i. p. 46.) : " When 

 we view an objett fteadily, we have acquired a habit of 

 direfting the optic axes to the point in view ; becaufe its 

 piftures falling upon the middle points of the retinas, are 

 then diftinfter than if they fell upon any other places ; and 

 fince the piftures of the whole objeft are equal to one 

 another, and are both inverted with refpett to the optic 

 axes, it follows that the pidtures of any collateral point 

 are painted upon correfponding points of the retinas." 



Dr. Wells is of opinion, that Dr. Smith's hypothefis for 

 the folution of this celebrated queftion is liable to other 



objeftions 



