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Chap. 8.] Gensanne—De Mov/ra — Amontons' Fire MM.

can say without pretending to prejudice any one’s merit, that I nevermet with any French or English man who had so much ingenuity andknowledge in mechanical, hydraulic, fire machinery principles, &c. as Ri-vatz.” (Gent, Mag. 1702, page 404.)

In 1734 M. Gensanne, a French gentleman, made some improvementson Savery’s engine, and by additional mechanism rendered it self-acting.The alternate descent of two vessels of water opened and closed thecocks, on much the same principle as that exhibited in Fludd’s pressureengine, page 354. (Machines Approuvees, tome vii, 222.) In 1740 M.De Moura, a Portuguese , accomplished the same thing by the ascent anddescent of a copper ball or float within the receiver; but the device wastoo complicated for practical purposes. It is figured and described bySmeaton in the Philosophical Transactions , vol. xlvii, 437, in the Supple-ment to Harris’s Dictionary of the Arts, and in other English works. In1766, Cambray de Rigny, an Italian, made some additions to Savery’sengine so as to make it in a great measure independent of manual assistance.Professor Francois, of Lausanne , having been consulted respecting thedraining of an extensive marsh between the lakes Neuchatel , Bienne andMorat, adopted a fire engine on Savery’s plan, and which he made self-acting by a more simple device than either of the preceding. A descrip-tion and good figure of his machine may be seen in the fourth volume ofthe Repertory of Arts, (1794) page 203. Nuncarrow’s improvement onSavery’s is described in the American Phil. Transactions, vol. i, 209, inTilloch ’s Phil. Mag. vol. ix, 300, and in Galloway’s History of the Steam-Engine. An English patent was issued in 1805 to James Boaz, and an-other in 1819 to Mr. Pontifex, both for improvements on Savery’s engine.For further information see the Repertory of Arts, Nicholson’s Journal,vol. i, 419, and the Journal of the Franklin Institute .

“ A commodious way of substituting the action of fire instead of theforce of men and horses to move machines,” was proposed in 1699, by M.Amontons, one of the earliest and most useful members of the French Academy of Sciences . He named his machine a fire mill. It resembleda large wheel, supported on a horizontal axis, but was composed of twoconcentric hollow rings, each of which was divided by partitions into adozen separate eells. The small or interior ring was at a considerabledistance from the axis, and the cells communicated with each other throughopenings made in the partitions and covered by valves or clacks. Thecells of the exterior rings had no communication with each other, but apipe from each connected them with the inner ones. The outer cellscontained air, and about one half of the inner ones contained water. Theobject was to keep ihis water always on one side, that its weight mightact tangentialiy, and so cause the wheel to revolve, and the machine con-nected to it. A furnace was built close to a portion of the periphery, andthe lower part of the wheel was immersed in water, to a depth equal tothat of the exterior cells. When the fire was kindled, the air in the cellagainst which the flame impinged became rarefied, and, by means of apipe communicating with an inner cell below the axle, forced the watercontained in that cell into an upper one. This caused that side of the wheelto preponderate, which brought another air cell in contact with the fire,and the fluid becoming expanded by the heat forced up the contents ofanother of the inner cells into a higher one, as before : in this way everypart of the periphery of the wheel was brought in succession in contactwith the fire, and the water in the inner cells kept constantly rising onone side of the wheel, thus causing the latter to revolve. The air in the