No. XXIII.
To set a clock as within a castle, the water filling the trenches about it; which shall show, by ebbing and flowing, the hours, minutes, and seconds, and all the comprehensible motions of the heavens, and counterlibration of the earth, according to Copernicus.
NOTE.
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.