THE career of this indefatigable investigator, as we announced last week, has just closed. Born in the second year of the present century, he has occupied a notable position in the scientific world for more than fifty years. Before he reached middle age he met with the terrible misfortune of losing his eye sight while trying venturesome experiments on the physiological effects of light. His scientific career seems to have become only more active in consequence! When we think of the ease and success with which certain chess players can, blind-fold, carry on some dozen or two simultaneous games, there seems little to surprise us in the mathematical career of Euler after he became blind. But the difficulties which stood in the way of the physicist, and which he successfully overcame, were of a far more formidable character. Had his chief investigations related to sound, the loss of eyesight might have but little interfered with them. But to carry out by the help of others' eyes a long series of investigations connected with Physiological Optics was a triumphal feat with which we know nothing to compare, except, perhaps, the composition of those marvellous master-works which Beethoven elaborated after he had become stone deaf.