BLINDNESS, a total privation of sight, arising from an obstruction of the func tions of the organs of sight, or from an entire deprivation of them.
This defect may arise from a variety of causes, existing either in the organ of sight, or in the circumstances necessary to produce vision. Blindness will be complete, when the light is wholly ex cluded ; or partial, when it is admitted into the eye so imperfectly, as to convey only a confused perception of visible ob jects. Blindness may again be distin guished into periodical or permanent, transient or perpetual, natural or acci dental, &c. but these distinctions do not serve to communicate any idea of the causes of blindness.
We find various recompenses for blind ness, or substitutes for the use of the eyes, in the Wonderfill sagacity of many blind persons, recited by Zahnius, in his " Gen ius Artificialis," and others. In some, the defect has been supplied by a most ex cellent gift of remembering what they had seen ; in others by a delicate nose, or the sense of smelling; in others, by an exquisite touch or a sense of feeling, which they have had in such perfection, that, as it has been said of some, they learned to hear with their eyes ; as it may be said of these, that they taught them• selves to see with their hands. Some have been enabled to perform all sorts of curious and subtle works in the nicest and most dexterous manner.
Aldrovandus speaks of a sculptor who became blind at twenty years of age, and yet, ten years after, made a perfect marble statue of Cosmo H. de Medicis ; and another of clay like Urban VIII.
Bartholin tells us of a blind sculptor in Denmark, who distinguished perfectly well, by mere touch, not only all kinds of wood, but all the colours ; and F. Gri maldi gives an instance of the like kind ; besides the blind organist, living in Pa ris, who is said to have done the same. The most extraordinary of all is a blind guide, who, according to the report of good writers, used to conduct the mer chants through the sands and deserts of Arabia.
James Bernouilli contrived a method of teaching blind persons to write.
An instance, no less extraordinary, is mentioned by Dr. new, in the " Transac tions of the Manchester Society." It is that of a person, whose name is John Metcalf; a native of the neighbourhood of :Manchester, who became blind at so ear ly an age as to be altogether unconscious of light :Ind its various effects. His em ployment in the younger period of his life was that of a wagoner, and occasion ally as a guide in intricate roads during the night, or when the common tracks were covered with snow. Afterwards he became a projector and surveyor of highways in difficult and mountainous parts ; and in this capacity, with the as sistance merely of a long staff, he tra verses the roads, ascends precipices, ex plores vallies, and investigates their seve ral extents, forms, and situations, so as to answer his purpose in the best manner. His plans are designed, and his estimates formed, with such ability and accuracy, that he has been employed in altering most of the roads over the peak in Der byshire, particularly those in the vicinity of Buxton, and in constructing a new one between Wilmslow and Congleton, so as to form a communication between the great London road, without being obliged to pass over the mountain.
Although blind persons have occasion, in a variety of respects, to deplore their infelicity, their misery is in a consider able degree alleviated by advantages pe culiar to themselves. They are capable of a more fixed and steady attention to the objects of their mental contempla tion, than those who are distracted by the view of a variety of external scenes. Their want of sight naturally leads them to avail themselves of their other organs of corporeal sensation, and with this view to cultivate and improve them as much as possible. Accordingly, they derive relief and assistance from the quickness of their hearing, the acuteness of their smell, and the sensibility of their touch, which persons who see are apt to disre gard.