himself to think it over again. He would then devote a part of the night to revolving the question again and again under all its aspects, to seek the cause of the failure and the means of future success."
His enthusiasm would sometimes put his assistants' patience to a rather severe test, and he would cry out, "Oh, if I could only see!" but as soon as success crowned his efforts, the indefatigable experimenter loved to express his gratitude. He cross-questioned Nature with more severity because he could only receive her answers by the voice of an interpreter. The thousand obstacles that presented themselves because of his infirmity only suggested a thousand precautions in order to surmount them. His inner vision was so preternaturally clear that he often corrected the observations of his assistants, and taught their eyes to see aright.
The love of scientific accuracy is not so much a mental as a moral quality. Plateau was possessed of a supreme love for truth, which not only made him accurate in his investigations and in the records of his experiments, but it made him careful not to judge others without a full knowledge of the facts. Always ready to ascribe scientific discovery to the right persons, he spared no pains to know who was the true discoverer.
The instructions which he gave to his pupils bore his own peculiar stamp. He used simple language and almost a conversational tone. His phrases were short, incisive, and clear, a fitting medium for the expressions of a mind so unclouded, so direct, and so concentrated. His talents as an experimenter were even more marked than as a speaker—more marked, because it is a far more uncommon gift.
He was an old-fashioned believer. The more deeply he "penetrated into the secrets of Nature, the more he inclined toward the mysteries of the supernatural order," says his biographer.
The picture of his home-life—his delight in and tenderness for his children in his early manhood, and the same gentle benevolence shown toward his grandchildren in his old age—is very beautiful.
As a scientist he is held in very high esteem by the greatest of his contemporaries. Honors were showered upon him by the great scientific societies of Europe. Such men as Arago and Faraday were glad to do him honor.
His earlier work was confined to the subject of the persistence of luminous impressions upon the eye and the determination of several simultaneous impressions under various conditions of motion. Many of the scientific toys of to-day are the outcome of facts and laws established by him, though he is not often accredited with these earlier discoveries. With the study of persistence of visual impression is so closely associated subjective color that
