[_A double-drawing Engine for weights._] The articles Nos. 25, 27, and 29 can only be taken as descriptive of elucidatory models, demonstrative of the applications of a certain principle, the result of condensation. For some unaccountable reason there has been a prevalent opinion that the Marquis was ignorant of condensation. If such an opinion is grounded on his not expressly alluding to it in the “Century,” then by the same rule it might be doubted whether he understood anything about steam! But as the “Century” was written to remind himself, and not to inform others of the _modus operandi_, it was sufficient for his purpose to particularise only the results. We can usually distinguish where he treads a beaten track, the result of reading, and where his course deviates into his “fire-water-work” experiments. The former generally has its parallel in some old author; but when the same rule is attempted to be applied to measure the others, we find we are dealing either with a new order of things, or else with sheer paradoxes of the most chimerical character. While, on the other hand, follow him in his own new track of experimental research, and we are rewarded at every step with a full and clear exposition of the wonderfully ingenious processes of inquiry by which he attained the perfection ascribed by him to his “Water-commanding Engine.” [Illustration: A double-drawing Engine] In the present article it is required that a weight shall take up double its own weight, not by the old rule of leverage, but “at the self-same distance from the centre.” In the subjoined diagram we have two cylinders C, B, connected at the lower end with a steam pipe, supplied with the steam-cock A. A cord passing over the drum wheel D, is connected at its ends with the pistons B, C; and the whole stands in a trough E. Steam having been admitted to B, and then cut off, condensation has ensued, the piston B has descended and C has been raised, and along with it a quantity of water. Here we may take the two pistons as representing “one hundred pound” each, and although they balance, yet we thus find “how to make a weight” under such circumstances, nevertheless, take up “two hundred pounds,” that is, including the water. A very similar kind of piston to the one here shown, is suggested by Fludd, Besson, and others, to be worked by a spiral spring, which being drawn to the bottom of a cylindrical vessel, water may be poured in above it, and being then tightly covered, with a lid having either an open jet or a tap in the centre, on releasing the spiral spring, the false bottom rising, and pressing the liquid, causes it to escape in a jet d’eau, gradually diminishing as the spring relaxes. The contrivance is elaborately illustrated in the 18th folio engraving of Besson’s “Theatrum Instrumentorum et Machinarum,” 1578; the Marquis, therefore, had only to substitute steam for the spiral spring. 26.