As to the fact of his supposing, when he first saw, that all objects whatever touched his eyes, Mr Che selden is also express in his testimony ; and it is dif ficult to admit, either that so accurate an observer could have been mistaken, or that the ingenious young gentleman, whose case he describes, could have been himself deceived, or have intended to deceive others on this point. If he had no previous concep tion of visible distance, it is in perfect conformity to the received philosophy of vision, that he should at first be unable to form any distinct judgment concern ing it ; for it has been clearly shevvn by Bishop Berke ley, and those who have followed him in this track of investigation, that our estimate of visible distance is not an original but an acquired faculty. That it is not like the perception of colour, or apparent magni tude and form, at once impressed upon the mind; but presupposes a complex process of mental investi gation, in which we compare together a variety of particulars made known by the eye, when we look at the same object at different distances ; such as its comparative distinctness or obscurity of outline, the brightness of its colours, its apparent bulk, the pecu liar adjustment by which we are conscious that the eye adapts itself to a variation of distance, and the change in the inclination of the axis of the two eyes, which a change of distance requires. On account of the great rapidity with which this mental induction, or comparison of particulars, is made, in consequence of constant habit, those who have long used their eyes are altogether unconscious of its ever having ta ken place. But it has been proved, in a most satis factory manner, by Berkeley and his followers, that the estimate of visible distance really depends upon such a mental investigation, or comparison ; and if this be the case, it is a necessary consequence, that when a person, who has been all his life totally blind, is first restored to sight, he will, for some time, be utterly unable to judge of distances, and will natu rally be inclined to believe, that the things which he sees touch his eyes, just as the things which he feels touch his skin.
We have the satisfaction to find this defence of the accuracy of Cheselden's interesting report con ' cerning his couched patient greatly corroborated by a paper of Mr Everard Home, published in the Phi losophical Transactions for 1807, and containing two cases of children born with cataracts, whom he re stored to sight by couching. These cases are much more in conformity with•the case of Cheselden's pa tient than those of Mr Ware, and clearly prove, that there is a considerable diversity in the degree of blind ness which cataracts produce. In the first case, the sight of the patient, a boy of twelve years of age, was so obscured, that he could discern light only, but neither colours nor forms. He was only imper fectly restored to vision ; but, as far as could be as. certained, he had no knowledge of visible forms after the operation, and judged all objects to touch his eyes. The other patient, a boy of seven years of age, could distinguish colours as well as light ; and, therefore, had some knowledge of distance. In him the operation was completely successful ; and he was so charmed with the new sense of seeing, that lie took every opportunity of removing the bandage from his newly couched eye. He could distinguish distance
immediately, but had long a very imperfect know ledge of forms. " A pair of scissars," says Mr Home, " was shewn to him, and he said it was a knife. On being told he was wrong, he could not make them out ; but the moment he touched them he said they were scissars, and seemed delighted with the discovery. On being shewn a guinea, at the dis tance of fifteen inches from his eye, he said it was a seven shillings piece ; but placing it about five inches from his eye, he knew it to be a guinea ; and made the same mistake as often as the experiment was re peated." The account adds, that, four days after the operation, he was allowed to go about ; when, on going to the window, he cried, " What is that moving ?" Mr Home asked him, what he thought it was ? he said, " A dog drawing a wheelbarrow. There is one, two, three dogs drawing another. How very pretty !" These proved to be carts and horses on the road, which he saw from a two pair of stairs window. At first, he called all regular shaped sur faces round ; but soon learned to distinguish those that were angular.
To persons who have been totally blind from their infancy, it is altogether impossible to impart any no tion or conception of light and colours ; the eye be ing the only avenue by which such a conception can reach the mind. This notion, however, seems to be the only one, of all that immense stock of ideas which we derive from sight, that is completely beyond the reach of a blind man's capacity. Of forms, the touch communicates the most accurate information ; and distance must be previously ascertained by touch, be fore it is made known by the eye. Even motion, the perception of which might seem peculiarly to belong to the eye, is only certainly ascertained by the touch; for the eye often considers motion to be real, when it is only apparent. If the ideas of the blind, there fore, be necessarily more limited than those of per sons who see, they have the advantage of superior accuracy and precision so far as they extend.
It is not, however, without much cultivation and care, that the blind can be enabled to make those ac quisitions, by which they may possess a rational source of enjoyment within themselves, and become useful and important members of society. In that state of mental darkness to which they are naturally exposed by the deprivation of so important a sense, they are objects of the liveliest compassion ; and call, from their more fortunate brethren, for all the ten 'derness and sympathy which enlightened humanity can impart. The language which Milton has put in to the mouth of Samson Agonistes is scarcely too strong for their unfortunate condition and was, no doubt, dictated by his own painful feelings : " 0 loss of sight, of thee I most complain ! Blind amongst enemies ! 0 worse than chains, Dungeon, or beggary, decrepid age ! Light, the prime work of God, to me's extinct ; And all her various objects of delight Annull'd, which might in part my grief have eas'd. Inferior to the vilest now become Of man or worm.