BALANCE FOE WEIGHING COIN 283 



motion, and the feeding slide pushes the lowest piece forward on to the weighing- 

 plate, the grippers meantime holding fast by the neck of the pendant, so as to keep 

 the plate perfectly steady; the dipping-finger is also at its lowest position, and 

 resting upon the knife-edge at the bottom of the slot in the pendent rod, thus keeping 

 tho beam horizontal, and the knob on the counterpoise-pendant in contact with the 

 agate point already mentioned. When the coin is fairly placed on tho weighing-plate, 

 the grippers let go their hold of the pendent rod, and the dipping-finger is raised by 

 its cam ; if then tho coin is too light, the coin end of the beam will rise along with tho 

 dipping-finger, and the counterpoise end will descend ; if heavy, the beam will remain 

 without motion, the agate point preventing it. As soon as the dipping-finger attains 

 tho proper height, and thus has allowed sufficient time for the weight of the coin to 

 be decided, the grippers close and hold the pendant, and consequently the scale or 

 weighing-plate, at the high level, if the coin has proved light, and been raised by the 

 excess of weight in the counterpoise ; and at the low or original level, if the coin has 

 proved heavy. One of the displacing slides now comes forward and passes under tho 

 coin, if it is light, and therefore raised to the high level ; but knocks it off, if 

 remaining on the low level, into tho ' heavy box.' Tho other displacing slide then 

 advances. This strikes higher than the first, and removes the light piece which the 

 other has missed, into the receptacle for the light coin. During these operations the 

 feeding-slide has brought forward another coin, and the process just described is 

 repeated. The attendant is only required to replenish the inclined plane at intervals, and 

 remove the assorted coin from the boxes. The perfection of the workmanship, and the 

 harmony of the various actions of the machine, will be best appreciated from the fact, 

 that 25 pieces are weighed per minute to the fineness of ^gth of a grain. This com- 

 bination of great speed and accuracy would not have been possible with a beam made 

 in the ordinary way, having the centre of gravity below the centre of action ; and it 

 was pronounced to be so by the late Mr. Clement, the constructor of Mr. Babbage's 

 Calculating Machine. But Mr. Napier overcame the difficulty by raising the centre 

 of gravity so as to coincide with the centre of action, which gave it much greater sen- 

 sibility ; and he provided the dipping-finger, to bring the beam to a horizontal position 

 after each weighing, instead of an influencing weight in the beam itself. 



The wear and tear of these machines is found to be very small indeed ; those sup- 

 plied in 1842 and 1843, and in daily use ever since, weigh with the same accuracy as 

 at first, although they may be said to have cost nothing for repairs. The principal 

 cause of this long-continued perfection is that the beam does not oscillate, unless the 

 coin is light, and even then the space passed through does not exceed the thickness of 

 the coin. 



In 1851, when the Moneyers were no longer masters of the Royal Mint, and the 

 new authorities began to regard the process of weighing tho coin in detail by hand as a 

 laborious, expensive, and inaccurate method, the firm of Napier and Son, at an inter- 

 view with Sir John Herschel, the Master, and Captain Harness, tho Deputy-Master, 

 received an order for five machines, to be designed to suit the requirements of the 

 Mint, which involved a complete change in the mechanical arrangement of the 

 machine as used at tho Bank, it being necessary to divide the ' blanks,' or pieces 

 before they are struck, into three classes, ' too light,' ' too heavy,' and ' medium,' or 

 those varying between certain given limits. It would occupy too much space to 

 attempt a description of the mechanical disposition of this machine, and it could not 

 be satisfactorily accomplished without the aid of drawings ; let it suffice, then, to say 

 that the displacing-slides are removed, and a long vibrating conducting-tube receives 

 the blanks as they are in turn pushed off the weighing-plate by the on-coming blanks ; 

 but, according to the weight of tho blank, so the lower end of the tube is found to be 

 opposite to one of throe openings leading into three boxes. The tube is sustained in 

 its proper position, during tho descent of the blank last weighed through it, by a 

 stop-finger, the height of which is regulated by a dipping-finger, which comes down 

 upon a knife-edge at the lower end of a slot in the pendent rod just when the grippers 

 have laid hold of the rod after the weighing is finished ; this finger thus ascertains 

 tho level which the knife-edge has attained, and as it brings down the stop-finger with 

 it, the guide-tube, which is furnished with three rests, as steps in a stair, vibrates 

 against the stop-finger, one of the three steps coming in contact with it, according to 

 the level of the stop-finger ; and the end of tho guide-tube takes its place opposite the 

 channel leading to the box in which the blank should be found. The counterpoise- 

 employed is less than the true standard weight, by the quantity which may be 

 allowed as the limit in that direction ; and in case a blank is too heavy, not only is 

 tho counterpoise raised, but a small weight, equal to the range allowed between tho 

 'too light' and 'too heavy,' is raised also; this small weight comes to rest on 

 supports provided for it when the beam is horizontal, and is only disturbed by a too 

 heavy blank. 



