In this manner his time was fully and usefully employed in the country, till, in 1775, when the act being passed for the better regulation of the gold coin, he was appointed stamper of the mooey-weights; au office conferred upon him, altogether unexpectedly, and without solicitation. Upon this occasion he removed to Lon don, where lie spent the remainder of his days, in the constant habits of cultivating some useful parts of philosophy and me chanism.
In 1778, Mr. Whitehurst published his Inquiry into the Original State and For mation of the Earth ; of which a second edition appeared in 1786, considerably enlarged and improved ; and a third in 1792. This was the labour of many years; and the numerous investigations necessary to its completion, were in them selves also of so untoward a nature as, at times, though he was naturally of a strong constitution, not a little to preju dice his health. When he first entered upon this species of research, it was nut altogether with a view to investigate the formation of the earth, but in part to ob tain,such a competent knowledge of sub terraneous geography, as might become subservient to the purposes of human life, by leading mankind to the discovery of many valuable substances which he con. mated in the lower regions of the earth.
May the 13th, 1779, he was elected and admitted a Fellow of the Royal So ciety. Before he was admitted a mem ber, three several papers of his had been inserted in the Philosophical Transac tions, viz. Thermnmetrical Observations at Derby, in vol. 57 ; An Account of a Machine for raising Water. at Ottlton, in Cheshire, in voi. 65; and Experiments on Ignited Substances, vol. 66: which three papers were printed afterwards in the collection of his works in 1792.
In 1783, he made a second visit to Ire land, with a view to examine the Giant's Causeway, and other northern parts of that island, which he found to be chiefly composed of volcanic matter : an account and representation of which are inserted in the latter editions of his Inquiry Dur ing this excursion he erected an engine for raising water from a well, to the sum mit of a hill, in a bleaching ground at Tullidei, in the county of Tyrone, which is worked by a current of water.
In 1787, he published An Attempt to ward obtaining Invariable Measures of Length, Capacity, and Weight, from the Mensuration of Time. His plan is, to ob tain a measure of the greatest length that convenience will permit, from two pendu lums whose vibrations are in the ratio of 2 to 1, and whose lengths coincide nearly with the English standard in whole num bers. The numbers which he has chosen show much ingenuity. On a supposition that the length of a second's pendulum, in the latitude of London, is 39g inches, the length of one vibrating 42 times in a minute, must be 80 inches ; and of ano ther vibrating 841imes in a minute, must be 20 inches ; and their difference 60 inches, or five feet, is his standard mea sure. By the experiments, however, the difference between the lengths 'of the two pendulum rods, was fbund tube only59,892 inches, instead of 60, owing to the error in the assumed length of the. second's pen dulum, 394 inches being greater than the truth, which ought to be 59.1- very nearly. By this experiment, Mr. Whitehurst ob tained a: tact, as accurately as may he in a thing adds nature, viz. the differ ence between the lengths of two pendu lum rods whose vibrations are known : datum from whence may be obtained, by calculation, the true lengths of pendulums, the spaces through which heavy bodies fall in a given time, and many other par. ticulars relating to the doetcniolgravita tion, the figure of the earth, &c.
Mr. Whitehurst had been at times sub ject to slight attacks of the gout, and be had for several years felt himself gradu ally declining. By an attack of that disease in his stomach, after a struggle of two or three months, it put an end to his laborious and useful life, on the 18th of February, 1788, in the 75th year of his age, at Ins house in Bolt Court, Fleet street, being the same house where ano ther eminent self-taught philosopher, Mr. James Ferguson, had immediately before him lived and died