It is worthy of remark that the incidental accounts of these two foreigners contain almost the only contemporary information we possess as to the character of the Marquis’s invention. English writers of the time are almost entirely silent about it; and when Dr. Hooke, the learned Secretary of the Royal Society, refers to the contrivance, it is in a tone of ridicule rather than of praise. Writing to Mr. Boyle, in 1667, he characterises the definition or description of the water-commanding engine as “so purely romantic that it would serve one rarely to fill up half a dozen pages in the ‘History of Fortunatus his Wishing Cap.’” ... “I was,” he adds, “since my return to London to see this engine, when I found Caltrop [Kaltoff], his chief engineer, to laugh at it; and as far as I was able to see it, it seemed one of the perpetual-motion fallacies; of which kind Caltrop himself, and two or three others that I know, are labouring at this time in vain to make, but after several ways; and nothing but costly experience will make them desist.”[13] [13] The Works of the Hon. Robert Boyle, v. 532. It is difficult to gather from the statements of Sorbière and Cosmo de Medici what was the precise nature of the Marquis’s hydraulic apparatus. There is no mention whatever of steam, either in their accounts or in that of Dr. Hooke; but the latter does not seem to have been allowed to examine the details of the machine. From the mention by Sorbière of the “four large buckets of water,” and by Cosmo’s secretary, of “four vessels of water,” it might possibly have been only an improved hydraulic apparatus, worked by a man instead of a horse. In order, therefore, to obtain a clue to the real nature of the machine we find it necessary to resort to the Marquis’s ‘Scantlings’ for his own account of its action, and we find it in article No. 68, which runs as follows:--