SKETCH OF A. F. J. PLATEAU. 697 



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 an- 

 swers 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 pe- 

 culiar stamp. He used simple language and almost a conversa- 

 tional 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 " pene- 

 trated 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 benevo- 

 lence 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 Fara- 

 day 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 mo- 

 tion. Many of the scientific toys of to-day are the outcome of 

 facts and laws established by him, though he is not often accred- 

 ited with these earlier discoveries. With the study of persistence 

 of visual impression is so closely associated subjective color that 



