350 



MINT 



coins per minute, Peculiarly admirable as are these machines, their perfection has 

 been greatly increased by improvements suggested by Mr. Richard Pilcher, who h;is 

 immediate charge of those in the Royal Mint. Mr. Pilcher, whose inventive genius is 

 only equalled by his desire to give to the public the benefit of his inventions, has ren- 

 dered these automaton balances serviceable to the Mint ; whereas, when they left the 

 hand of Mr. William Cotton, they were of great service to the Bank of England 

 alone, for there only two determinations, or in fact one determination is necessary. 

 Jn that institution it is required to show that the coins issued by it are not below 

 tho legal weight for circulation, whereas the Mint must guarantee that coins leave 

 its works neither above nor below the limits fixed liy law ; hence the necessity 

 for the incorporation of Mr. Pilcher's improvements with Mr. Cotton's beautiful in- 

 vention. 



Fig. 1540 exhibits a view of a model of Cotton's automaton machine, for the 

 purpose of illustration ; and it should be mentioned that Messrs. D. Napier and Sons 

 are tho makers of the machines actually in use. 



1540 



The whole theory of this balance rests on the fact that the centre of gravity and 

 the centre of action are in one line : either being disturbed, the balance is no longer 

 equal. The machine gains its motion from a shaft fixed to the ceiling of the room. 

 Steam contained in a boiler exists under an ever-varying pressure, arising from the 

 amount of work which it may be necessary for the engine to perform, or from the 

 irregular combustion of the fuel as well as from other causes. Since it is of tho 

 utmost importance that the automaton balance should be made to maintain a uni- 

 form pace, Messrs. Napier and Sons found it necessary to drive the shaft which 

 gives it motion by a small atmospheric engine, which is placed in tho weighing- 

 room. It has been found that a chamber may be kept equably exhausted of air, 

 if tho atmosphere be admitted to it by a xiniformly-weighted valve. Such a chamber 

 is used in the Mint for other purposes, and Messrs. Napier conducted from this a 

 pipe, by the agency of which the atmospheric engine is worked with a far more 

 even and steady motion than could be obtained by steam ; in fact, the exhausted 

 chamber becomes a regulated spring, which softens down the variations in the motion 

 of the steam-engine. The shaft supported by the ceiling conveys its motion to the 

 weighing-machine by a line which, passing over friction-wheels, circulates round a 

 stepped-wheel, which runs loose on the shaft communicating with J. The line is 

 maintained with sufficient rigidity by a weight which is suspended at the end of tho 

 lever carrying friction-wheels. The weight is just sufficient to insure the continuous 

 working of the machine, but it is so light as to permit the line to slip in the event of 



