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Rh his sagacity, and impulses from his zeal. Of all men who ever lived, he was perhaps the most prolific in mechanical invention. New instruments, or useful modifications of those already in use, flowed from him by the dozen. An arithmetical machine, a triple writing-machine, a deep-sea sounding machine, a wind-gauge, rain-gauge, hygrometer and odometer, a system of telescopic telegraphy, a "water-poise," a "weather-clock," and a species of microphone, were all due to his ingenuity; besides important improvements in astronomical and other instruments—telescopes, quadrants, micrometers, diving-bells, barometers, thermometers, and balances. He speculated curiously on memory, and calculated the number of ideas of which the human mind is susceptible, estimating it at three thousand one hundred and fifty-five million seven hundred and sixty thousand! He constructed a model for the rebuilding of London after the great fire, which was approved, although not adopted; and was the architect of Hoxton Hospital and other buildings. He read before the Royal Society commentaries on Ovid's "Metamorphoses," Plato's "Atlantis," and Hanno's "Periplus," interpolating these critical excursions between geological theories and astronomical observations. To him was due the ingenious idea of measuring the force of gravity at different altitudes by the rate of vibration of a pendulum of a given length; as well as the determination (so far as the actual state of chemical knowledge permitted it to be determined) of the true function of the air in combustion and respiration. His zeal carried him to the length of making, in an exhausted receiver, his own person the subject of his observations—"the only experiment of that kind," his biographer naïvely remarks, "I think ever tried."

At the present time, when weather prophecies have come to form a recognized part of our complex social machinery, it would be ungrateful to omit noticing that Hooke was the first to propose a scientific system of meteorological forecasting. His scheme, as might be expected, had for its basis the close association (remarked by him among the earliest) of changes of weather with barometrical variations; which, he writes to Boyle, October 6, 1664—

If it continue to do as I have hitherto observed it, I hope it will help us one step toward the raising a theorieal pillar or pyramid, from the top of which, when raised and ascended, we may be able to see the mutations of the weather at some distance, before they approach us; and thereby being able to predict and forewarn, many dangers may be prevented, and the good of mankind very much promoted.

The means recommended by him for the furtherance of this noteworthy object were the same in principle as those now in use at all the meteorological observatories of Europe and America. Two hundred years, however, had to elapse before they could be profitably employed.