_London, Published by Charles Knight, Ludgate Street._ ] [Illustration] HARRISON. John Harrison was born in May, 1693, at Foulby, in Yorkshire. His father, who was a joiner, trained him from an early age to the same business; but he soon began to study machinery. He turned his attention to the mechanism of clocks; and, to obviate the irregularities produced in their rate of going by variations of temperature, he invented the method of compensation, employed in what is now called the _gridiron_ pendulum, before the year 1720. This contrivance consisted in constructing a pendulum with bars of different metals, having different rates of expansion so as to correct each other: it is described in all popular treatises on physics. By this means it is stated that he had, before the year above-mentioned, constructed two clocks which agreed with each other within a second a month, and one of which did not vary, on the whole, more than a minute in ten years.[10] Footnote 10: Folke’s Address to the Royal Society, Nov. 30, 1749. This success induced him to turn his attention to watches, or rather to time-keepers for naval purposes. It would be impossible without the help of plates to render intelligible the rise and progress of his methods, for which we must refer the reader to treatises of Horology. His first instrument was tried upon the Humber, in rough weather, and succeeded so well that he was recommended to carry it to London, for the inspection of the Commissioners of Longitude.