200
blowpipe apparatus. It is very well made, and the Jurydeemed it worthy of Honourable Mention.
Doi/berg (Meeklenburg-Sehwerin). Balance, to carryone kilogramme in each pan. This balance is in manyrespects very well constructed: but the middle knife-edgeis supported by two agate planes, and the bearings of theknife-edge on the planes are rather short, both of whichcircumstances are defects. The oscillation of the pans ischecked by hair-brushes, which on turning a handleascend till the ends of the brushes touch the under-sidesof the pau : in this arrangement there is reason to appre-hend that loose hairs might attach themselves to theunder-sides of the pans, and so lead to an error in theweighing.* The pans are suspended from plates of steel,having plane surfaces, which rest upon the extreme knife-edges.
A Prize Medal was awarded to Mr. Dolberg.
Bech.hr (Netherlands , No. 8*3, p. 1147 . Balance,capable of carrving one kilogramme in each pan. Thebeam is a sipgle bar, the middle knife-edge being sup-ported on two agate planes.T The contrivance for liftingthe pans and beam when not in action is ingenious, inas-much as the motion is slow at the time the beam is depo-sited on the middle support, and the agate planes fromwhich the pans hang on the knife-edges; but it is unsteadyin a lateral direction. There is also reason to apprehendthe extreme knife-edges would not touch the agate planesin the same parts in successive weighings. The methodof attaching the pans to the brass rods by which they aresuspended, in such a manner as effectually to guard againstupsetting the pans wherever the weight may be deposited,is extremely simple and ingenious. The Jury consideredit worthy of Honourable Mention.
Nesses (Denmark , No. 20, p. 135G). A large balanceto carry 10 lbs. (4-54 kilogrammes): the middle knife-edge is cut away in the middle, so that the bearings ofthe edge on the middle plate arc too short. The pans aresuspended from plates having concave surfaces, whichform of plate is objectionable. They arc not supportedindependently of the beam, when the balance is not inaction.
The excentric motion for putting the balance in actionhad been injured, so that it could not be tried.
A small balance exhibited by Nissen, capable of carry-ing more than 100 grammes. The middle knife-edge inthis, also, is cut away, so that the ends only touch theplane surface on which it rests. The balance in other irespects resembles Robinson’s balances, except that the 'middle knife-edge rests upon two planes, and that the jplane surfaces are of steel instead of agate. It is fur-nished with Wollaston’s contrivance for checking theoscillation of the pans and beam.
The same exhibitor has also a small assay-balance.
The Jury considered Mr. Nissen as deserving Honour-able Mention.
Littman* (Sweden , No. 15, p. 1350). In this balancethe index is at one end of the beam. In addition to thisindex there is another pointing upwards, the end of whichis viewed through a compound microscope, having adivided scale or glass in the focus of the eye-piece. Thiscontrivance for reading oif the extreme portions of thebalance during its oscillation is far inferior to a graduatedscale, attached to the beam of the balance, observed witha compound microscope having a single wire in the focusof the eye-piece. It also adds greatly to the bulk of thebalance-case. The J ury considered this balance deserving iHonourable Mention.
Viberg Sweden and Norway , No. 14, p. 1350) exhibits (a chemist’s balance, which the Jury considered worthy ofHonourable Mention, it being well adapted for the pur-poses it lias to perform.
Coin-}Yei'jhing Machines.
We will now turn our attention to another class ofbalance, recently introduced, viz., coin-weighing machines.Of these there are three in the Exhibition—one exhibited
* This contrivance is greatly inferior to Wollaston’s foreffecting the same purpose.
f This is not a good construction.
by W. Cotton, Esq., late Governor of the Bank of Eng-land; a second by Captain Smith ; and a third made byDeleuil (France , No. 100, pp. 1178—1180); this lastinstrument was designed by Baron Shcuier.
Before proceeding to the particulars of these beautifulinstruments, it may be well for a short time to dwell uponthe want which has called them into existence, as kindlyexplained by William Miller, Esq., of the Bank of Eng-land. All sovereigns brought into the Bank of England by the public are weighed singly, and this is found to beabsolutely necessary ; else the stock of sovereigns in theBank would very soon fall below the legal current weightof 122^ grains each. The Bank , therefore, is compelledto weigh all the gold coin it receives singly, to guardagainst loss.
In June, 1842, the Queen’s Proclamation was issued,commanding all persons to cut and deface whatever goldcoin was found to be below the current weight. Beforethat time the light sovereigns, though they were rejectedby the Bank , were accepted almost'everywhere for theirfull value, and the public were not disposed to criticisevery nicely the Bank ’s weighing, as the rejection of theirmoney occasionally, when it was really of the currentweight, or the issuing it to them a trifle below the weight,was of small consequence ; for, though it might occasiona little trouble, it entailed no loss. But it was quite adifferent affair when their sovereigns were cut as well asrejected, so that they were obliged to sell them as bullion,sometimes at a loss of three-pence or four-pence a-piece;or when, as was sometimes the case, they received sove-reigns at one counter of the Bank which were cut and re-turned to them when tendered at another. The publicthen, as might be expected, were very angry ; but therewas no help for it. The Bank had provided the bestscales that could be procured: they had the most expe-rienced weighers : they re-weighed singly every gold coinin their stock, amounting to upwards of £S,OUU,000, andweeded it of all the light pieces that could be detected, at aloss of between £3,500 and £4,000; but the evil remained.Sovereigns were still issued at one counter which wererejected and cut at another.
This did not arise from any fault cither of the Bank orof its officers, hut from the inherent difficulties in theoperation of weighing so accurately as was necessary, orwith the same result, in a limited time, even with thebest-constructed scales. Some of the causes of errorMr. Cotton ascertained to be—differences in the weightsmade (notwithstanding the Mint stamp attached to them),of considerable amount in relation to the degree of cor-rectness required; currents of air acting unequally uponthe scale-pans; a constant diminution of the weight of onepan, by the act of placing and displacing the coins to beweighed, by which the equipoise was even- moment de-stroyed; the striking of the scale-pans upon the counter:difference in the judgment of the weighers; the shorttime which could be allowed for the operation ; failing ofthe eye-sight, flagging of the attention, and sleepinessfrom the monotony of the employment; difference in therate of vibration of the beams; defects of principle in theconstruction of the scales, to obviate which would havedestroyed their simplicity and marred their general use-fulness.
All these difficulties (and they were great) were over-come by Mr. Cotton ’s machine ; and since the year 1844,out of the large number of 80,000,000 of pieces whichhave been weighed, not a single source of error has beenmade out against them. Some few sovereigns are stillweighed as they are received from the public by the com-mon scales; but such are never re-issued by the Bankuntil they have passed through the machines, which ex-tract from them about two per cent, of lightness. TheBank sustains the loss upon these unavoidable errors, inpreference to the loss of time, the trouble, and the vexa-tion which the re-issue of them as they were receivedfrom the public would occasion to all parties.
”\Ve now proceed to the description of Mr. Cotton ’smachine.
It consists of a square brass box: on the top is placeda hopper to hold the sovereigns to he weighed. Thishopper is a long trough, placed at an angle of about 45'