Then, as regards the Engine itself, it was required by the Act of Parliament, “that a model thereof be delivered to the Lord Treasurer or Commissioners for the Treasury for the time being, at or before the 29th day of September, 1663,” and the same to be “put into the Exchequer and kept there;” a requirement which he was certain to obey punctiliously, not only to avoid dispute, but because nothing was easier for him to perform, through the agency of Kaltoff. Another remarkable point referring to his Engine is that he concludes the 98th article of his Century, which alludes to it, by saying:--“I call this a semi-omnipotent Engine, and do intend that _a model thereof he buried with me_.” And lastly, there was his practical demonstration on a large scale. As early as May 1654, we have an intimation of his being in treaty for works at Vauxhall. Not long afterwards we find his workman Kaltoff settled there, and in one of his Petitions he explicitly mentions having spent “£9,000 on buildings and improvements,” and at least “£50,000 in trying experiments and conclusions of art in that Operatory:”[M] thus actually curtailing his personal comforts to fulfil his engagements with all those persons who confided in his promises to perfect his novel undertaking. His works and Engine were examined and noticed in 1663, by the French traveller M. Sorbière; in 1666 or 1667 by the eminent mathematician Dr. Robert Hook, whose cynicism unfortunately thwarted his judgment; in 1669, by the Grand Duke, Cosmo de Medici; and we find it still in existence in September, 1670, being then alluded to in a letter written by Walter Travers, a Roman Catholic priest.[N] We have, therefore, certain evidence that the Marquis of Worcester’s Engine was in full operation for at least seven years, and that one of the conditions of the Act of Parliament obliged him to deposit a model in the Exchequer. His own estimate of its value may be judged by his gladly giving up for the promised tithe of it to the King, his claim on Charles the First equal to £40,000, in lieu thereof.[O]