Erect vision from an inverted image / by B.F. Joslin.

  • Joslin, Benjamin F. (Benjamin Franklin), 1796-1861.
Date:
[1845]
Catalogue details

Licence: Public Domain Mark

Credit: Erect vision from an inverted image / by B.F. Joslin. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    one moment reversed with respect to its position twelve hours previou ^ yet, from a comparison of objects on its surface, we perceive no chan r. of position. So forcibly and habitually is this impressed upon our mine ( that thousands, who are convinced of the earth’s rotation, find it dii j cult to realize, whilst the mass of mankind are with difficulty convinc (, of the fact; and no man would have discovered it, if no world but tl js had existed. Whether we consider the perception of contiguity as resulting direct j[ from the contiguity of the parts impressed, or mediately through the mu t, cular sense, it is evident that this perception must be one of the earlic jv elements of our knowledge of position, and that there neither is, nor c; be, any kind of eye so constituted as to make erect objects appear invei je ed, either with respect to the earth or an erect observer. « If we had made no reference to muscular action, the greater part oftl gi foregoing reasoning would have been the same; and it is true, that, aft p a very short experience, we can judge of contiguity and angular distani nJ from simultaneous impressions. The variable distinctness of these f je different parts of the retina affords data. But as this distinctness dimi [q ishes equally in all directions from the centre, it affords no data for imm ^ diately determiningin what direction we should move the eye, in order li; obtain a distinct view. This leads us to the second division of our su n; ject. |s Let us now consider the question in its second sense. This is a kirt of practical sense in which we may speak of knowing the position I objects, i. e., knowing in what direction to roll the eye, or move the hariL in order to trace the object from top to bottom, or bottom to top, from rig |( to left, or left to right, &c. I The particular modes in which different directions and different degreiL of angular distance are estimated by muscular action, it is not essentii here to consider. In the “ Physiological explanation of the beauty form,”* I have recognized in the vision of objects, the necessity of tratii ing them by means of the ocular muscles. This art, with its resu]tir| knowledge and pleasure, is acquired only by experience. The young ii^ fant, though created with mental faculties for the estimation of form art magnitude, and for the enjoyment of beauty and grandeur, has no actuL perception of either. In the investigation before us, we are chiefly coii cerned with the mode of estimating direction. Suppose a child who has acquired the use of his hands, but who h4 been blind from his birth, to have the sense of sight given him by a su gical operation. At first he would be utterly unable to point towards an object, of whose situation he had no knowledge except that given by tl eye. For example, suppose him looking at a star through a tube hel near his eye by another individual. He would be unable on a first a tempt, to direct his finger or arm toward the star, and would be as liabl to move it in the opposite direction. If a higher and a lower star wei visible through the same tube, and his finger were already directe toward one of them, he would be utterly unable to decide as to what kin of volition was necessary in order that his finger should move towar the other. He would be liable to the mistake of moving it up instead c down, to the right instead of the left, and in directions at all possible ai Transactions of the Medical Society of the State of New York.