258

BALANCES, BY OERTLING, DOVER, FOX, &c.

[Class X.

5u lbs. in each pan. Many of them have probably neverbeen surpassed, in the construction of the beam, knife-cQ&es, planes opposed to them, permanence of the adjust-ments and beauty of workmanship; yet in all, the positionof the beam, when loaded with the weights to be com-pared, is shown by a long index nearly in contact with agraduated arc, although for several years other andgreatly superior methods of determining the position ofthe beam have been in use, such as by a graduated arcattached to one end of the beam, and viewed through acompound microscope having a horizontal wire in thefocus of the eye-glass, or by a mirror attached to thebeam, in which the reflected image of a scale is viewedthrough a telescope.

In the balances exhibited the beam and pans are sus-pended on knife-edges, more or less in length, with thesingle exception of Mr. Fox’s balance, in which the beamhas pivots, the conical ends of which play in hollow agatecones of larger angle.

There is no example of the balances constructed underthe direction of Gauss and Weber, and described in the“ Gottingen Transactions,” in which the beam is sus-pended by two watch-springs, and each pan by a singlewatch-spring; nor of either of Steinheil’s balances, in■which the beam and pans are suspended by wires or silkribbons; nor of the balances first (Professor Miller be-lieves) invented by Steiuheil and used by Knpffer in com-paring the Russian standard of weights, in which thebeam carries two small steel spheres in the middle, restingupon a steel plane, and a sphere at either end, upon whichrest the plane or slightly concave spherical surfaces of theplates from which the scale-paus are suspended.* *

There are a variety of contrivances for checking theoscillation of the beam and pans when in action: none ofthem can compare in simplicity and efficiency with theapparatus invented by Wollaston, aud used by the lateT. C. Robinson, Barrow, Dover, and by most of theEnglish makers of balances, and also by Nissen, of Copen-hagen , the only foreign maker who appeal's to have madeuse of it.

In nearly, perhaps in every instance, when the divisionsof the scale, to which the index of the balance points,were numbered; the division to which the index pointswhen the beam is horizontal is marked zero, and the scalenumbered 1, 2, 3, &c., to the right and left. This methodis most inconvenient, and frequently leads to error. Thenumber of the divisions ought to run all the same way,and need not begin with zero, it being far better tonumber that division to which the index points, when thebeam is horizontal, 10, 20, or some multiple of 10, for thepurpose of avoiding the trouble, perplexity, and liabilityto error, attendant upon the necessity of noting numbers,in addition to whether the numbers are positive or nega-tive. This remark is of general application to all instru-ments to which scales are affixed.

L. Oertling (No. 334, p. 440} exhibits a large balancehaving a beam 3 feet in length, coated with platinum,fand capable of carrying 50 lbs. (equal to 25 - 4 kilo-grammes) in each pan. The beam, a pierced rhomb, isconstructed so as to give great strength in proportion toits weight. Any tendency to lateral yielding is counter-acted by casting the beam with edge bars.

The whole length of the middle knife-edge rests upon aplane surface of steel: the three knife-edges are long.Plane surfaces of steel, from which the scale-paus are sus-pended, rest upon the extreme knife-edges. When not inaction the beam and the steel planes from which the scale-pans hang, are supported, so as not to be in coutact witheach other. The frame for supporting the beam and pansis extremely well contrived ; so also is the mechanism forlifting it.

lie exhibits also a balance capable of carrying one kilo-gramme in each pan. The beam of this balance, which is16 inches long, is coated with palladium;! the three

* See KupfFer’s work on the Comparison of Standards”for a description of this balance.

t These beams were coated by T. II. Ilenrv. Esq.. F.R.S.,by a peculiar process, in which the electric current wasemployed in depositing these metals. It would seem, from

knife-edges, as well as the plane upon which the middleknife-edge rests, and the planes from which the pans aresuspended, arc of agate, so that the whole instrument isunaffected by acid vapours. The beam is graduated, andsmall differences of weight are determined by a smallweight that can be placed upon parts of the graduatedbeam. The beam and paus are supported, excepting whenin action. The adjustments of the knife-edges, in thedirection of the length of the beam, are as few as possibleto be very permanent. The knife-edges are not capableof any adjustment after leaving the artist’s hands in adirection perpendicular to the length of the beam. As faras the beam and knife-edges are concerned, a betterbalance has probably never been constructed. lie exhibitsalso a smaller balance: the beam is 14 inches long, similarto the former in construction, and capable of carryingabout 1,000 grains. A Council Medal was awarded toMr. Oertling.

Dover (No. 344, p. 449) exhibits a balance, which inconstruction is similar to the balances constructed by thelate T. C. Robinson, and, in execution, fully equal to thebalances made by that most excellent artist. The beamis 10^ inches long, and is capable of carrying about 2,000grammes iu each pan.* The three knife-edges are ofsteel, the planes opposed to them being made of agate.The final adjustments, both in the direction of the lengthof the beam and iu a direction perpendicular to it, areeffected by a cut at each end of the beam making an angleof about 45 3 with the axis of the beam, which may bewidened by means of a screw. This is an excellent modeof adjustment, succeeding perfectly, and proved to be verypermanent when confined to extremely narrow limits. Ifthese limits be exceeded, as they sometimes are inunskilful hands, the end of the beam is cracked anddestroyed.

Mr. Dover has substituted chains with long links forsilk threads, for suspending the pans, and has added aningenious contrivance for supporting glass tubes inweighing.

A Prize Medal was awarded to Mr. Dover.

Fox (No. 377, p. 451) exhibits a balance for extremelysmall weights, which has instead of a knife-edge at themiddle, an axle ending in conical points, which pointsplay in conical holes (the angle of the cone in the holesis, of course, greater than the angle of the cone of thepivots'). The attraction of a magnet brings the beamexactly to zero before weighing. In order to overcomethe friction, of which much is introduced by the con-struction of the balance, there is an instrument for raspingon the case.

Marriott (No. 341, p. 449) exhibits a chemical balance,the beam of which is made of a wide bit of wood (fir', withinterstices cut out so as to leave a strongly framed net-work. The knife-edges do not appear to admit of anyadjustment. The scale-pans are suspended from doublehooks of wire hanging on the end of the knife-edges.This instrument is a curiosity: it is stated by the makerto be sensible to the 100th of a grain. It is a good ex-ample of a make-shift for a balance, when at a distancefrom good workmen.

De Grave, Short, and Fanner ( No. 333, p. 446,) ex-hibit two assay-balances, apparently of very good work-manship, but not adjusted,! and a large number of com-mercial balances of various kinds, weights, and measuresof capacity and length.

Bachk > United States , No. 395a, p. 1462).—Large ba-lance, capable of carrying 56 lbs. (equal to 25*4 kilo-grammes' in each pan. The knife-edges are square barsof steel. Each bar is fitted into a socket attached to thebeam, having a rectangular notch, so that any one of thefour edges of the bar may be used as a knife-edge.J "The

this successful application, that the same process is appli-cable to graduated instruments.

* A similar balance, finished by Mr. Dover, was usedrepeatedly by Professor Miller to weigli 5,760 grains, andwas not in the slightest degree injui’ed.

+ The centre of gravity is too high to admit of usingthem.

+ In the event of one of the edges being damaged thisarrangement is of great service.