In the year 1728, when King George visited the University, lie expressed a de sire of seeing so remarkable a person ; and accordingly our professor attended the King in the senate, and by his favour was there created doctor of laws.
Dr. Saunderson was naturally of a strong, healthy constitution ; but being too sedentary, and constantly confining himself to the house, he became a valetu dinarian : and in the spring of the year 1739 he complained of a numbness in his limbs, which ended in a mortification in his foot, of which he died the 19th of April that year, in the 57th year of his age.
There was scarcely any part of the mathematics on which Dr. Saunderson bad not composed something for the use of his pupils. But he discovered no in tention of publishing any thing, till, by the persuasion of his friends, he prepared his Elements of Algebra for the press; which, after his death, were published by subscription, in two vols. 4to. 1740.
He left many other writings, though none perhaps prepared for the press. Among these were some valuable com ments on Newton's Principia, which not only explain the more difficult parts, but often improve upon the doctrines. These are published in Latin, at the end of his posthumous Treatise on Plosions, a va luable work, published in 8vo. 1756. His manuscript lectures too, on most parts of natural philosophy, might make a consi derable volume, and prove an acceptable present to the public, if printed.
Dr. Saunderson, as to his character, was a man of much wit and vivacity in conversation, and esteemed an excellent companion. He was endued with a great regard to truth, and was such an enemy to disguise, that he thought it his duty to speak his thoughts at all times with unrestrained freedom. Hence his senti ments on men and opinions, his friend ship or disregard, were expressed with out reserve ; a sincerity which raised him many enemies.
A blind man, moving in the sphere of a mathematician, seems a phenomenon difficult to be accounted for, and has ex cited the admiration of every age in which it has appeared. Tully mentions it as a thing scarcely credible in his own master in philosophy, Diodotus, that he exer ciscd himself in it with more assiduity after he became blind ; and, what he thought next to impossible to be done without sight, that he professed geome try, describing his diagrams so exactly to his scholars, that they could draw every line in its proper direction. St.
Jerome relates a still more remarkable instance in Didynius, of Alexandria, who, though blind from his infancy, and there fore ignorant of the very letters, not only learned logic, but geometry also, to a very great perfection, which seems most of all to require sight. But if we con sider that the ideas of extended quantity, which are the chief objects of mathema tics, may as well be acquired by the sense of feeling as that of sight, that a fixed and steady attention is the principal qualifica tion for this study, and that the blind are, by necessity, more abstracted than others, (for which reason, it is said, that Demo critus put out his eyes, that he might think more intensely,) we shall perhaps find reason to suppose, that there is no branch of science so much adapted to their circumstances.
At first, Dr. Saunderson acquired most of his ideas by the sense of feeling; and this, as is commonly the case with the blind, he enjoyed in great perfection. Yet he could not, as some are said to have done, distinguish colours by that sense ; for, after having made repeated trials, he used to say it was pretending to impossibilities. But lie could with great nicety and exactness observe the smallest degree of roughness, or defect of polish, in a surface. Thus, in a set of Roman medals, he distinguished the genuine from the false, though they had been counterfeited with such exactness as to deceive a connoisseur who had judged from the eye. By the sense of feeling, also, he distinguished the least variation ; and he has been seen in a garden, when observations have been making on the sun, to take notice of every cloud that inter rupted the observation, almost as justly as they who could see it. He could also tell when any thing was held near his face, or when he passed by a tree at no great distance, merely by the different impulse of the air on his face.