Blindness, implies either a partial or total privation of sight, proceeding from some defect of the organs of vision, or an impaired 6tate of their functions. Hence it may be either total, partial, transient, periodical, or nocturnal. The causes of blindness are likewise various, such as weakness, or decay of the optic nerves, preternatural conformation of the organs, external violence, malignant effluvia, poisonous liquids dropt into the eye, too frequent exposure to intense heat, long confinement in dark places, etc.
As we propose to treat of the principal diseases of the eye, under the heads of Cataract, Gutta-eRena, and Sight, we shall here only observe, that those unfortunate persons who "are born blind, or lose their sight in infancy, seldom recover that important faculty, and ought therefore to be educated for such pursuits as are adequate to their individual capacities. It is, indeed, equally cruel, and inconsistent with good policy, to suffer these pitiable beings frequently to spend a vagrant life, and remain in the darkest ignorance. On the contrary, it has been uniformly observed, that tho privation of one sense renders the others comparatively more acute and useful. Hence blind persons generally hear better, and possess a more accurate sense of touch, than those who enjoy all their sensitive faculties; and we have also many instances of the poetical and philosophical talents displayed by the former.
With a view to contribute our share towards alleviating the severe lot of such unfortunate individuals, we shall here communicate an in-vention of Mr. Thomas Gren-v;lle, organist, of Ross, in Herefordshire ; who, in the year 1770, received a premium of fif-teen guineas; and, in 1785, for some additional improvements, the silver medal, from the Society for the Encouragement of Arts, he. It is remarkable, that the ingenious inventor is himself deprived pf sight; and that by the use of his machine, any blind person may be taught the elements of arithmetic, namely, addition, subtraction, multiplication, division, reduction, and the rule of three, whether in money, weights, or measures of every kind, as perfectly as it may be performed on paper. His apparatus being of a simple construction, and so contrived that it may be of service in teaching the art of reckoning, to young children, in a very easy and entertaining manner; we shall first give an account of this machine, as represented in the subjoined cut, and then conclude with a description of its me-chanism.
It consists of a box nineteen inches square in the clear space within, and near two inches deep, divided into cells, containing the figures, lines, etc. hereafter described, necessary for performing the rules of arithmetic. The lid or cover of the box, which serves as a leaf, or slate, is pierced full of holes in parallel rows; the first row has eighteen large, and seventeen small holes, alternately placed; the second row, eighteen small holes, placed under the above large ones ; the third, as the first, and so on alternately, thirty-five rows, the whole cover being full, and containing three hundred and twenty-tour large holes, and six hundred and twelve small ones, which make an exact square. The figures are represented by pegs with cubical beads, and distinguished by pins placed on one side in the following manner :—One, is expressed by a pin's point on the right-hand; two, by the same in the middle; and three, by having it on the left-hand ; four, five, and six, by pins' heads in the above three different situations ; seven, eight, and nine, by crooked pins, or staples, in the same, manner: the cypher is understood by a plain peg without any mark. On the top of each pi printed the figure which it represents, to render the work intelligi-ble to any person that may see it, without being acquainted with the marks. These pegs are made to fit the large holes. Pieces of brass wire, bent to a right angle, about half an inch from each end, and made to fit the small holes, serve for the purpose of lines, to separate the different parts of the work.
The box contains twenty-eight partitions, situated as in the following cut, ten of them to hold figures, and the others for the lines of different lengths.
A, The box, with its several divisions, containing the different pegs, bars, etc. with which the rules in arithmetic are to be performed.— B, The cover, which, when turned back, and standing on its feet as represented, shews the holes wherein the pegs and bars are occasionally placed to exhibit the value of the figures.—C, The pegs, marked in such manner as to enable the blind person to distinguish by the touch, what each peg is intended to represent, when placed in the holes in the cover B.
A complete specimen of this machine may be seen in the Repository of the Society, Adelphi-build-ings, London.
With respect to the education of the blind, we have already remarked, that it deserves public sympa-♦ thy, and the interposition of the legislature ; as their natural industry, and persevering application, will enable them to overcome the greatest difficulties, and amply repay the trouble and expence bestowed on their mechanical, or literary, acquirements. To strengthen their faculties, and preserve their health, Hind children should never be suffered to remain idle, so that during the hours of recreation, they ought to take suitable exercise, such as riding on horseback, walking out in fair weather, the use of dumb-bells, the bath-chair, etc. - In regard to diet, their meals should be temperate, light, and of easy digestion. Vegetables the most farinaceous, and least acescent, should be preferred to animal food. Neither fermented liquors, nor ardent spirits, should be given them, except in cases of general debility. Tea is likewise pernicious; and their regular drink ought to consist of equal parts of milk and water: a little chocolate, and coffee, may occasionally be granted 3 but infusions of balm, sage, or ground-ivy, are more wholesome. Tobacco and snuff must be absolutely prohibited 3 and, on the whole, blind persons should neither be too much restricted to the observance of a rigid system of diet, nor allowed to eat and drink whatever is suggested by their own fancy : in the former case, they are apt to' become pitiable slaves to custom 3 and, in the latter, it is a shameful dereliction of duty in those whom Providence has enabled to see, and direct their affairs.
Blindness, in farriery, is a disease incident to the eyes of horses, but more particularly to those of an iron grey, or dapple-grey, colour 3 and is supposed to proceed from riding them too hard, or. backing them at too early an agey This disorder may be discovered by the walk or step, which, in a blind animal, is always uncertain and unequal, when led; but, if he be mounted by an expert horseman, an apprehension of the spur may induce him to move with more freedom, so that the blindness can scarcely be perceived. A horse may also be known to have lost his sight, if observed constantly to prick up his ears, and move them backwards and forwards, on hearing any person enter the stable.
The ordinary cause of blindness in horses, is attributed by Dr. Lower to a spongy excrescence growing in one, and sometimes in two or three places of the coloured part of the iris, or which being ultimately over-grown, covers the pupil when the horse is brought into the light, but again dilates on returning him to a dark stable.— See Eyes of Horses.