S e , and, therefore, the apparent magnitude of objects, seen by aoncave lens, is less than the true ; the object is also less luminous,ra secn through such a lens, than without it; because the

y s being rendered more divergent, a less quantity enters thePupil of the eye, than otherwise would do: for the picture is al-J* a ys more or less bright, according as it is made by a greater orss quantity of rays. Lastly, it appears from what has been said,tat when a concave lens EF, cannot be applied, we may stilluect distinct vision, by lessening the distance between the objectIM tbe f 'F e » for >f plain, if OB be situated at OB, the image atJw. will recede to im, upon the retina, and be distinct, in the same“'anner as when made so by the lens EF. On the other hand,ben the cornea or crystalline is too flat, &c. (as often happens byan object OB, (iig. 5,) placed at the same distance from theye PC, as before, will have the rays Co, Co, after refraction in*5.'-ye, proceed to a focus beyond the bottom of the eye, inb ,c h> if a hole were made (in an eye taken out of the head) flicys would actually go on, and form the image im ; which imageUs f> therefore, be very confused and indistinct on the retina.0 remedy this defect, a convex lens GH, is applied, which“Uses the diverging rays C a, Cb, to fall less diverging upon they e > or as if they came from a point more remote, as c ; by whichbeans the focal distance is shortened, and the image duly formedn the retina at IM, by which distinct vision is produced. Ilence,e apparent place of the object is at c, and is more distant than the, rue place at C ; and its apparent magnitude OB is greater than’ e true, because the converging rays O a, B b, are by this lenster refraction made to unite sooner than before, and so to con-ain an angle OYB greater than the true OPB. The object ap-pears through a convex lens brighter than without, because by thispaeans a greater quantity of rays enter the pupil; for the rays no,°> are by the lens made to enter in the directions ar, hr, whichre nearer together, and leave room for more to enter the pupil allround between o and r. As the image of the object painted onretina is greater or less, so will tile apparent magnitude of theeject be likewise ; or, in other words, the angle 1PM, (fig. 6,)uptended by the image is always equal to the angle OPB sub-° J ,- Ct a ,V he and therefore the image IM will

tho SV?PlK"r al , ° f he ° b ^ ct ° B - He » ce fol 'ows, thatthe ingle Oi B undti whicii an object appears is the me'Knre nf itc

apparent magnitude. Therefore objects of different magnitudeas OB, AC, DE, which subtend the same angle at the eye havethe same apparent magnitude, or form an equal image in the bot-tom of the eye. Ilence it is that objects at a great distance havetheir magnitude diminished proportionally : thus the object DEAmoved to DE appears under a less angle DYE, and makes a lessUllage on the retina, as is'shewn by the dotted lines. The anglesapparent magnitude OAB, OCB, (fig. 7,) when very email, aretheir sines, and therefore as the sides OC and OA, or BC and BA;-hat is, the apparent magnitude of die object OB, at the distancesPl-l and BA, is inversely as those distances; or its magnitude at CI s to that at A as AB to CB. The more directly any object iss ituated before the eye, the more distinctly it will appear ; be-muse those rays only which fall upon the eye near its axis can be‘■oiivened to a point in the bottom of the eye on the retina, andberefore that part of the image only which is formed by the di-s ect Pencil of rays can be clear and distinct; and we are said tot P e an object by such a pencil of rays, but only to look at it bye others which are oblique. Suppose A, B, C, (fig. 8,) repre-^ nt three pieces of paper stuck up against the wainscot of a roomth , height of the eye; if then a person places himself so beforev * U>, and shutting iiis right eye view r s them with his left, it ist|)P’. rem arkable that the paper B, whose pencil of rays falls upon0r e insertion D of the optic nerve DE, will immediately vanishan |'Appear, while the two extreme papers C and A are visible;the altering the position of the eve, and its distance, any oft 0 .J^Pers may be made to vanish, by causing the pencil of raysthe 3 011 the P°int D. Why the rays of light should not excitesensa d°n of vision in the point'D, where the fibres of thei s , Jr* begin to separate and expand every way to form the retina,f 0r q eas y to s ay. But it is worth notice, that the nerve DE isIiq u lat rea * on Phced on one side of the eye, where only the ob-w>a y J?>' s come, the loss of which Is not considerable, and nofared .■ 1 or hinders the perfection of sight: whereas had it en-v n tlie middle of the bottom of the eye, it had rendered use-n. iv—. No 2 j 4 _

less all the direct rays, by which the most perfect and distinct vi-sion is effected; and we could have had only a confused and im-perfect perception of objects by oblique collateral rays. Thelaws of vision, brought under mathematical demonstration, makethe subject of optics, taken in the greatest latitude of the word ;which is commonly used, in a more restrained sense, for the doc-trine of direct or simple vision, performed by rays passing direct-ly, or in- a straight line, from the object to the eye. SeeOptics.

VISITATION, in law, an act of jurisdiction whereby a supe-rior, or proper officer, visits some corporation, college, church, orother public or private house, to see that the laws and regulationsthereof are duly observed. Among us, visitation is that officeperformed by the bishop in every diocese once in three years, orby the archdeacon every year, by visiting the churches and theirrectors throughout the whole diocese, See.

VISMEA, a genus of the dodecandria trigynia class and orderof plants. Calyx five-leaved, inferior; corolla five-petaled;stigmas five; nectary two or three-celled. There is one species,a native of the Canaries.

U1ST, NOBTH, one of the Western Islands of Scotland , inInverness-shire, between Harris on the N. and Benbectila on theS. from which last it is separated by a narrow channel, which isdry at low watef.

UiST, South, another of the Hebrides , in Inverness-shire, whichlies between Barray on the S. and Benbecula , on the N. and is 32miles long, and from 9 to 10 broad.

VISTULA, or WE1SEL, a large river of Poland , which tak-ing its rise in the mountains S. of Silesia, vi- its Cracow, Warsaw ,&c. and continuing its course northward, falls into the Baltic seabelow Dantzic.

VITAL, in physiology, an appellation given to whatever mini-sters, principally to the constituting or maintaining life in the bodiesof animals: thus the heart, lungs, and brain, are called vital parts;and the operations of these parts by which the life of animals ismaintained are called vital functions.

VITERBO, a town of Italy , in Patrimonio, 20 miles S. E.of Orvielo, and 34 N. N. W. of Rome . Lon. 12. 26. E. Lat.42. 15'. N. _ „ , ,

VITEX, the Chaste-Tree ; a genus of the didynamia an-giospermia class of plants, with a monopetalous, ringent, and bila-biated flower, each lip of which is trifid ; the fruit is a quadrilocu-lar, globose berry,- containing four seeds. There are fourteen

Sp ViTis, in betanv, a genus of the class pentandria, and ordermonogynia; natural order, Personate.' Petals cohering at thetop, shrivelling; fruit a berry with five seeds. There are twelvespecies.; the most important of which is,

V. Viniff.ra, or Common Vine, which has naked, lobed.sinuated leaves. There are many varieties, all propagated eitherfrom layers or cuttings, the former of which is greatly practisedin England, but the latter is preferable. In choosing the cuttings,you should always take such shoots of the last year’s growth asare strong and well ripened ; these should he cut from the oldvine, just below the place where they were produced, taking aknot, or piece of the two years wood to each, which should be.pruned smooth ; then you should cut off the upper part of theshoots, so as to leave the cutting about sixteen inches li-r.g. Whenthe cuttings are made, if they are not then planted, they should beplaced with their lower part in the ground in a dry soil, layingsome litter upon.their upper parts to prevent them.from drying:in this situation they may remain till the beginning of April;when tliev should be taken out and washed from the filth theyhave contracted ; and if very dry, should stand with their lowerparts in the water six or eight hours, which will distend their ves-sels, and dispose them for taking root, If the ground be strongand’inclined' to wet, open a trench where the cuttings are to beplanted, which should be lilted with lime-rubbish, the better todrain off tire moisture: then raise the borders with fresh light earthabout two feet thick, so that it may be at least a foot above tl alevel of the ground : then open the holes at about six feet distancefrom each other, putting one good strong cutting into each bole,which should be laid a little sloping, that their tops may inqline tothe wall: but it must be put in so deep, as that the uppermosteve niav be level with the surface of the ground. Having placed

J io A the