282 BALANCE FOB WEIGHING COIN 



' BAT.fturCB FOB WEIGHING COTK, introduced at the Bank of England in 

 the year 1841, requires an especial notice. 



Mr. William Cotton, then Deputy-Governor, and during the two succeeding years 

 Governor of the Bank, had long regarded the mode of weighing by common hand- 

 balances with dissatisfaction, on account of its injurious effect upon the 'teller, 1 or 

 weigher, owing to the straining of the optic nerve by constant watching of the beam- 

 indicator, and the necessity of reducing the functions of the mind to the narrow office 

 of influencing a few constantly repeated actions. Such monotonous labour could not 

 be endured for hours together without moments of forgetfulness resulting in errors. 

 Errors more constant, although less in amount, were found to be due to the rapid 

 wearing of the knife-edges of the beam ; currents of air also acting upon the pans 

 produced undesired results ; and even the breath of the ' teller ' sometimes turned the 

 scale ; 8P that in hand-weighing the errors not unfrequently amounted to rd, and 

 even i grain. At the very best, the hand-scale working at the rate of 3,000 per six 

 hours could not indicate nearer than ^th grain. 



Upon taking into consideration the inconveniences and defects of the hand-weighing 

 system, Mr. Cotton conceived the idea that it might be superseded by a machine de- 

 fended from external influences, and contrived so as to weigh coins as fast as by hand, 

 and within the fourth of a grain. He subsequently communicated his plan to Mr. 

 David Napier, of York Road, Lambeth, engineer, who undertook the construction of 

 an experimental machine. Its capabilities were tested and reported upon by Mr. 

 William Miller, of the Bank. The result was most satisfactory : more ' automaton 

 balances ' were ordered ; and from time to time further additions have been made, so 

 that at present there are ten in daily operation at the Bank of England. But it was 

 not without a struggle that the time-hallowed institution of ' tellers ' passed away. 

 There were interests opposed to the introduction of improved, more ready, and less expen- 

 sive methods ; and it required all Mr. Cotton's energy of character, the influence of 

 his intelligence in mechanics, as well as that arising from his position in the Direction, 

 to obtain the adoption of an invention by which a very large annual saving has been 

 effected. 



The mechanical adaptation of the principles involved in the Automaton Balance, as 

 contrived by Mr. Napier, may be shortly explained : The weighing-beam, of steel, is 

 forked at the ends, each extremity forming a knife-edge ; and in the centre the fulcrum 

 knife-edge extends on each side of the plate of the beam, and rests in hollows cut in 

 a bowed cross-bar fixed to the under side of a rectangular brass plate, about 12 inches 

 square, which is supported at the corners by columns fixed to a cast-iron table raised 

 a convenient height on a stand of the same metal. To form a complete enclosing 

 case, plates of metal or glass are slid into grooves down the columns. When the beam 

 is resting with its centre knife-edge in the hollows of the cross-bar just referred to, 

 its upper part is nearly on a level with the under-side of the brass plate, in which a 

 long slot is made, so that the beam can be taken out when the feeding slide-box, and 

 its plate, which covers this slot, are removed. On the top of the covering plate of 

 the feeding slide a tube-hopper is placed, and a hole in the plate communicates with 

 the slide ; another hole is pierced in the same plate exactly over one end of the beam, 

 upon the knife-edges of which a long rod is suspended by hollows formed in a cross- 

 bar close to its upper end, where the weighing platform is fitted. A rod is also sus- 

 pended at the other end of the beam in a similar manner ; but instead of a weighing- 

 plate, it has a knob at top, which, when the beam is horizontal, comes into contact 

 with an adjustable agate point. The lower end of this pendent rod is stirrup-shaped, 

 for holding the counterpoise. Two displacing slides are provided, one on each side of 

 the feeding-slide, and at right angles to each other ; and a gripping apparatus is fixed 

 to the under side of the brass top-plate, arranged so as to hold the pendant on which 

 the scale-plate is fitted during the change of the coin. A dipping-finger is also at- 

 tached to the frame of the gripping apparatus, its end passing into a small slot in the 

 pendent rod, and acting upon a knife-edge at the lower end of the slot. There are 

 four shafts crossing the machine ; the one through which the power is applied is 

 placed low and at the centre, and carries a pinion which gears with a wheel of twice 

 its diameter on a shaft above ; this wheel gears with two similar wheels fixed to shafts 

 on each side of the centre. Cams for acting upon the feeding slide, through the 

 medium of a rocking frame, are carried by the shaft placed at the end of the machine 

 where the counterpoise hangs, and the other two shafts on the same level bear cams 

 for working the gripping apparatus, the dipping-finger, and the displacing slides. 



Having described, as clearly and as popularly as wo can, the general features of the 

 mechanism, we will proceed to indicate its manner of action. Suppose, then, the 

 hopper filled, and a hollow inclined plane about two feet long, which has been added 

 to the hopper by the inventive genius of one of the gentlemen in the weighing-room, 

 also loaded its whole length with the pieces to be weighed, the machine is set in 



