We have no certain key to any of his inventions, if we except two specimens of his cipher writing. One exists in the British Museum,[3] and there is a deciphered letter in the Bodleian Library, Oxford.[4] [3] See engraving and account of it in _The Life, Times, and Scientific Labours of the Marquis of Worcester_, 8vo. p. 398. 1865. [4] Ibid, page 180. His noblest invention, that which must for ever embalm his memory in the breasts not alone of Englishmen, but of all classes throughout the civilized world, was in operation at Vauxhall from 1663 to 1667, during his life time, and appears to have been working as late as 1670. It was ordered by the Act granted him, "that a model thereof be delivered to the Lord Treasurer or Commissioners for the Treasury for the time being, at or before the 29th of September, 1663; and to be put into the Exchequer, and kept there." And in the 98th article of the "Century," alluding to this same engine he says--"I call this a _semi_-omnipotent engine, and do intend that a model thereof be buried with me." Yet, strange to say, neither the one model nor the other, although zealously searched for, has come to light: and so little attention did this invention, notwithstanding its surprising utility, excite in the 17th century, that all the account we have of it, besides that by the inventor himself, is the briefest possible notice given by two foreign travellers, Sorbière in 1663-4, and Cosmo the third, Grand Duke of Tuscany, in 1669. It is satisfactorily ascertained, however, that upwards of seventeen persons, all living in 1663, were more or less acquainted with the Marquis's mechanical operations at Vauxhall, and must have seen the great water-engine at work, if only as a novelty, and a matter of curiosity. Returning to the "Century of Inventions," we find it to be a journal of the fruits of its noble author's study of mechanical philosophy for nearly forty years, so that in it we may almost trace the youth and age of his mental capacity. Viewed through a modern medium we might feel disposed to discredit the genius of a man who could contrive so many curious alphabets for secret writing as those he mentions, but such systems were extensively practised in political and private correspondence during the Civil war period to baffle the curiosity of political opponents. What may be called mechanical tricks were also much in vogue, such as singing and flying birds, artificial figures and horses, and curiously contrived watches, cabinets, locks, and keys. Unless we bear in mind the taste of the age, we shall read with surprise such an announcement as the following, in the 88th article in the "Century":--