Beyond all question the Marquis of Worcester’s prime invention, the _Water-commanding Engine_, was erected and at work from 1663, to the year 1670, during which time it had been made the subject of an Act of Parliament; had been published in the _Century_, in brief outline; also noticed in a separate pamphlet, copies of which are exceedingly rare; and likewise in large posting bills. Besides which a model was deposited with the Chancellor of the Exchequer as required by the Act. It was also the subject of much correspondence. That it excited the attention of intelligent sight-seeing travellers we ascertain from the Diaries published first by M. Sorbière, and five years later by Cosmo de Medici. And after the noble inventor’s decease, his warm-hearted and enthusiastic widow brought herself under priestly censure for her active endeavours “to enrich herself by the great Machine;” on which, alas! both had built reasonable, but such as were at that time considered extravagant, expectations of present fortune and future fame. With the Marquis of Worcester this invention was no idle fancy, no mere experiment, no amateur work, no casual, doubtful trial, and was not lightly estimated by himself. He had by practice so thoroughly satisfied himself, that, long after 1655, amidst all his troubles, without his notes, and to oblige a friend, he wrote off, _con amore_, three distinct accounts of his invention, under the titles of, “A fire water-work;” “A semi-omnipotent engine;” and lastly, “A stupendous water-work.” How it happens that the Marquis of Worcester should have been wholly unnoticed for his inventions by contemporaries it is difficult to offer anything like a sufficiently reasonable or satisfactory conjecture. But surprise might seem to vanish when such diarists as John Evelyn and Samuel Pepys, with all their curiosity and all their apparent pleasure in recording scientific novelties, although they name the Marquis, notice Worcester House, and mention Vauxhall, never so much as hint at one invention by the Marquis of Worcester. When these gossips had nothing to say, conjecture may well cease to promise a satisfactory solution.