The three last inventions may justly be considered as the most important of the whole "Century," and when united with the 68th article, they appear to suggest nearly all the data essential for the construction of a modern steam-engine. The noble author has furnished us with what he calls a "definition" of this engine; and although it is written in the same vague and empirical style, which characterises a large portion of his Inventions, it may yet be considered as affording additional proofs of the above important fact. The Marquis's "definition" is exceedingly rare, as the only copy known to be extant is preserved in the British Museum.--It is printed on a single sheet without date, and appears to have been written for the purpose of procuring subscriptions in aid of a Water Company, then about to be established. "A stupendous, or a water-commanding engine, boundless for height, or quantity, requiring no external, nor even additional help or force to be set, or continued in motion, but what intrinsically is afforded from its own operation, nor yet the twentieth part thereof. And the engine consisteth of the following particulars:-- 'A perfect counterpoise, for what quantity soever of water. 'A perfect countervail, for what height soever it is to be brought unto. 'A _primum mobile_, commanding both height and quantity, regulator-wise. 'A vicegerent or countervail, supplying the place, and performing the full force of man, wind, beast, or mill. 'A helm or stern, with bit and reins, wherewith any child may guide, order, and control the whole operation. 'A particular magazine for water, according to the intended quantity, or height of water. 'An aqueduct, capable of any intended quantity or height of water. 'A place for the original fountain or river to run into, and naturally of its own accord incorporate itself with the rising water, and at the very bottom of the aqueduct, though never so big or high. 'By divine providence, and heavenly inspiration, this is my stupendous water-commanding engine, boundless for height and quantity. 'Whosoever is master of weight, is master of force; whosoever is master of water, is master of both: and consequently to him all forcible actions and atchievements are easie.'"