A tide-mill was several years back exhibited in the Museum of that very ingenious mechanic, Mr. G. J. Hawkins; and a similar prime mover has been suggested for the purpose of winding a clock for a bell signal station on the Northern coast of England. An astronomical machine as described by the Marquis, must be provided with two barrels, each possessing a maintaining power sufficient for the correct performance of the whole. In addition to the line that supports the weight, or maintaining power, each barrel must be provided with a revolving pulley resembling those used for old thirty-hour clocks; with chains passing over their axis; and the chains being attached to large floats of wood will be alternately raised or depressed by the ebbing and flowing of the tide; and thus in succession wind up the weights which form the maintaining power of the clock. The clepsydræ, or hydraulic clock, was in general use among the ancients, and a stream of water was frequently employed to give motion to planetary machines. No. XXIV. How to increase the strength of a spring to such a degree as to shoot bombasses and bullets of an hundred pound weight a steeple height, and a quarter of a mile off and more, stone bow-wise, admirable for fire-works and astonishing of besieged cities, when, without warning given by noise, they find themselves so forcibly and dangerously surprised. NOTE. The strength of a compound spring formed of two metals may, by the application of heat, be increased to any given power. _Rationale._--Iron possessing an expansive power of 1/95, and brass being only 1/60, the weaker metal will be bent by that whose power of expansion is greater, and the impulse of the spring increased in an equal ratio. No. XXV. How to make a weight, that cannot take up an hundred pound, and yet shall take up two hundred pounds, and at the self same distance from the centre; and so, proportionally, to millions of pounds. NOTE. This is indeed paradoxical, and so completely contrary to every established principle or rule in science, that we may fairly set it down among the number of those inventions which, by partaking so highly of the marvellous, have contributed to bring the whole _Century_ into disrepute. No. XXVI. To raise a weight so well and as forcibly with the drawing back of the lever, as with the thrusting it forwards; and by that means to lose no time in motion or strength. This I saw in the arsenal at Venice. NOTE. The mere application of a crank, such as is used for the _foot-lathe_, acting upon a drum and fly-wheel, with a chain attached to move a second lever or upright sliding bar, will fully effect the object here described. No. XXVII.