Robert Hooke's Water Current Meter, Circa 1663

A water current meter is shown to have been built in 1663 by Robert Hooke (1635 - 1703), the author of Hooke's Law of Elasticity, and the first Curator of Experiments at the Royal Society of London. No drawing of that meter is known to exist, but the type of rotor and the revolution-counting facilities that Hooke had used thereon were the same as he had shown in a drawing of one of his deep sea sounding devices. A reproduction of that drawing is presented in the article. This is the earliest current meter to have been found so far in which use has been made (as in modern current meters) of a freely-rotating sensor with facilities for observing the number of turns the sensor made within a measured period of time. Features of the current meter built by Reinhard Woltman in about 1790, are so similar to those of Hooke's meter, that it is suggested that Woltman had duplicated Hooke's meter. Several other velocity-measuring devices conceived between the times of Hooke (1663) and Woltman (1790) are described briefly.