E A L 



211 



B A L 





sisting of Tartars, Greeks, Jews, Russians, and Ar- 

 menians, amounts to 3000. Eat Long. 31 24', 

 North Lat. 44 3S'. See Reuilly's Travel" into the 

 ' Crimea, and wjpng the Shores of the Black Sea, in 

 1803, chan. vi. (x) 



BALiEN T A, in Zoology, the while, a genus of 

 mammiferous animals, which in the Linnsean system 

 ranks in the order Cete of the class Mammalia, but 

 in the method of Ray, and the system of Lacepede, 

 constitutes a tribe of cetaceous fishes. See Ceto- 

 ior.Y. {/) 



BALiEN'OPTERA, a subdivision of the whale 

 tribe, formed into a new genus by Lacepede, and in- 

 cluding three species, distinguished from the bahenae 

 in having longitudinal folds under the throat and 

 belly, and dorsal fins. See Lacepede, Ifistoire Na- 

 tnrelles des Cetacees, p. 120; and Diet ionnaire des 

 Sciences Naturelies, torn. iii. p. 442. ( f) 



BALAKLAVA. See Balaclava. 



BALANCE, the name of a simple machine for 

 ascertaining the weight of any body, or for finding a 

 quantity of any substance equal to a given weight. 

 The balance has generally been arranged among the 

 mechanical powers, but it is evidently only a particu- 

 lar species of the lever in which the two arms are 

 equal, and in which there will be an equilibrium n lien 

 the power and weight are equal. 



The balance consists of a horizontal beam, which 

 turns round an axis or centre of motion exactly 

 in the middle of the beam. The two halves of the 

 beam, on each side of the axis, are called the arms 

 of the balance. From the two extremities of the 

 beam, called the points of suspension, are hung two 

 icales, in one of which is placed the substance to be 

 :d, and in the other are placed weights of a 

 known magnitude. The equality of the weights in 

 the two scales, or the perfect equilibrium of the ba- 

 lance, is known from the horizontal position of the 

 beam. In the common balance, where the whole 

 machine is suspended from the axis of motion, a slen- 

 der arm, called the tongue of the balance, rises per- 

 pendicularly from the centre of the beam, and points 

 to a particular part of the handle by which the 

 whole is suspended when the beam is horizontal. 



In balances where very great accuracy is required, 

 the beam is not supported by suspension, but lias a 

 fine edge of steel for its axis, which rests upon steel 

 planes. The horizontal position of the beam is in 

 this case determined, by observing when the extremi- 

 ties of the arms point to the zero of two ivory scales 

 fixed in the mahogany frame in which the instrument 

 is placed, the line joining the two zeros having been 

 previously placed in a horizontal position, by levels 

 fixed in the mahogany frame. The beams of these 

 delicate balances sometimes consists of a plain cylin- 

 drical rod, of a double cone, whose vertices form the 

 points of suspension, or of a frame in the form of a 

 rhombus. 



In constructing an accurate balance, it is necessary, 

 1. That the tico points of suspension , and the axis or 

 sentre if motion,, should be in the same straight line. 

 The energy of any weight in turning a lever round 

 its fulcrum is proportional to the perpendiculars let 

 fall from the fulcrum upon a vertical line passing 

 through the points of suspension. When the points of 



suspension, therefore, and the centre of motion, are not Balance. 

 in one line, the perpendiculars let fall upon the verti- ' v ' 

 cal lines are equal only when the line joining the 

 points of suspension is truly horizontal. In every 

 other position, the perpendiculars will be unequal, 

 and there will not be an equilibrium between equal 

 weights. When the points of suspension and the 

 centre of motion, however, he in the same straight 

 line, the perpendiculars upon the vertical lines must 

 be equal, in every position of the bsam, and there 

 will always be an equilibrium between equal weights, 

 the beam being supposed without weight. 2. The 

 points of suspension must he precisely equidistant 

 from the centre of motion, or, what is the same 

 tiling, the arms of the balance must be exactly of 

 the same length. It is obvious, that when the arms 

 v are unequal there cannot be an equilibrium between 

 equal weights, as the one weight acts at the extre- 

 mity of a longer lever than the other. 3. 'The centre 

 of gravity of the beam should be placed a little below 

 the centre of motion. If the centre of gravity of the 

 beam coincides with the centre of motion, the beara 

 will rest in any position in which it is placed, whether 

 it is unloaded or loaded with equal weights. If the 

 centre of gravity is above the centre of motion, the 

 beam will be overset by the slightest disturbance. 

 But if the centre of gravity is below the centre of 

 motion, the beam will not rest in any but a horizon- 

 tal position, and when disturbed will recover this po- 

 sition with a degree of facility proportioned to the 

 distance between the centres of motion and gravity. 

 The nearer, therefore, that the centre of gravity i 

 to the centre of motion, the more easily will the equi- 

 librium be disturbed, and consequently the more de- 

 licate will be the balance. 4. The beam should be as 

 light as possible, hut at the same time so strong as 

 not to change its form uhen the scales are loaded to 

 a maximum. It is evident, that the friction upon the 

 centre of motion will be diminished by the lightness 

 of the beam, and that the inertia of a light beam will 

 be more easily overcome by a small weight than the 

 inertia of a heavy one. 



Having thus stated very briefly the precautions 

 that are necessary in the construction of a delicate 

 balance, we shall proceed to describe three of the 

 best balances that have yet been made. The two 

 first were made by the celebrated Mr Troughton, 

 and the last by Messrs Miller and Adie, mathematical 

 instrument makers, Edinburgh, (o) 



In Figure 1. AB represents the scale-beam in its Troujrh- 

 most perfect state, as made by Mr Troughton. A ,ons ka- 

 strong mahogany box contains the whole ; it has p ,lte ; 

 drawers below for holding weights, &c. ; and a long f - 1# 

 one behind, wherein the beam is packed, when out 

 of use or in carriage. There are doors in the ends 

 through which the pans, or scales, are loaded and 

 unloaded, and through another at the top the beam 

 may be taken out. The front and back are of plate 

 glass. On the upper surface of the drawer depart- 

 ment are shewn two spirit levels, L, L by means of 

 which, and screws below, the balance is easily ad- 

 justed to its due position. There passes through the 

 box, a little below the levels, an iron rod, having at 

 each end a handle, by which it may be turned round. 

 One of these is seen in the figure at H. This rod 



