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 gave striking evidence of the genius which could only be quenched by death. It will be remembered that the inadequacy of his proposed chronometer had been the chief obstacle to the acceptance by the States-General of his method of taking longitudes at sea. Now, in the second half of the year 1641, it occurred to him, as is confirmed beyond question by Viviani, who was present, though the idea is generally ascribed to Christian Huyghens, of adding a pendulum to the then very imperfect clocks, as regulator of their motion. As this was sixteen years before Huyghens made known his invention of pendulum clocks, priority indisputably belongs to Galileo. But it was only permitted to the blind master to conceive the great idea—he was not to carry it out. It was his intention to employ the eyes and hands of his son Vincenzo, a very clever mechanician, to put his idea in practice, and he told him of his plan. Vincenzo was to make the necessary drawings according to his father's instructions, and to construct models accordingly. But in the midst of these labours Galileo fell ill, and this time he did not recover. His faithful pupil, Castelli, who probably foresaw the speedy dissolution of the revered old man, came to see him about the end of September, 1641. In October, on the repeated and urgent invitation of Galileo, Torricelli joined Castelli and Viviani, not to leave the Villa Arcetri until they left it with Galileo's coffin. Torricelli was then thirty-three, and the old master had discerned his eminent talents from a treatise on the theory of motion which he had sent him. Castelli was