The cylinder _b_, is in this engine placed over a boiler _n_, and if we suppose the piston _p_ made to fit air-tight, it will be evident, that it must be driven up by the action of the steam beneath, should a sufficient supply of heat be applied; when this is effected, the condensible vapour may be reduced to its original bulk, by the introduction of water from the cistern _i_. In the working engine however, the ascent of the piston is effected by the action of the lever _e g_, acting on the fulcrum _f_. To the end _g_ of this lever or working beam is attached the pump-rod _h_, and it will be evident that whenever that preponderates over the piston _p_, that the latter must be drawn up. On the readmission of the steam, a new supply of condensing water is introduced by turning the cock _l_, and the pressure of the atmosphere above the piston being unbalanced by any resistance beneath, the end _e_ is again depressed, and the pump-rod again elevated. The pipe _g_ is employed to carry off the condensing water, which would otherwise accumulate within the cylinder; and the small forcing pump, with its rod _v s_, supplies the condensing cistern _i_, by the pipe _t_. At the beginning of the last century, the atmospheric engine had made considerable progress in the mining districts, and in 1718, the patentees agreed to erect an engine for the owners of a colliery, in the county of Durham, where several hundred horses had previously been employed. Mr. Henry Beighton, who was engaged as an agent in this concern, materially improved the engine by making it self-acting, and divesting it of nearly all the complicated machinery, which had been previously employed for that purpose. A very simple and at the same time ingenious mode of illustrating the operations of an atmospheric steam-engine will be found in the annexed apparatus, suggested by Professor Brande, and employed in his lectures at the London Institution. [Illustration] The glass tube and bulb _b_ is shewn with its piston _a_, the rod being hollow and closed by a screw _c_. If steam be generated by the spirit lamp _d_, the air will speedily be expelled, and after this is effected, the screw _c_ may be closed, and a working stroke produced by artificial condensation. We come now to a new and distinct era in the history of this important invention, and in noticing the labours of Mr. Watt, we may almost speak of his engine as the gigantic offspring of a hand giving birth to an automaton, no less powerful than that of the fabled enchanters of the olden time.