HOROLOGY. 



Fig. 8. shews a balance according to a 

 construction used by Arnold, and speci- 

 fied by him to the commissioners of longi- 

 tude. The expansion weights are cylin- 

 drical, and are adjusted upon the arm by 

 screwing: and there is an inner rim up- 

 on which three weights are adjusted by 

 sliding. These serve to regulate the go- 

 ing of the time-piece in different posi- 

 tions. 



If an uniform ring, with two or more 

 radii placed at equal regular distances, 

 and in all other respects alike, were to be 

 poised on its axis, as a balance, no part 

 would preponderate; but ii would remain 

 at rest in any position ; and if we suppose 

 the axis itself to be a spring, such as a 

 piece of stretched wire, and we overl >ok 

 the difference of tension in the wire, 

 which might arise from the weight of the 

 balance itself, in different positions, it is 

 obvious that all the vibrations of that ba- 

 lance, through equal arcs, would be per- 

 formed in equal times, whether the ba- 

 lance were made to vibrate parallel to the 

 horizon, or in any other position. But 

 in the balance of a time-piece, the pivots 

 of its axis bear very differently, accord- 

 ing to the position of the chronometer; 

 and it requires some management to make 

 the frictions the same, whether the axis 

 be turning on one of its tnds, or upon the 

 two cylindrical faces of the pivots. And 

 still more than this, since the balance it- 

 self has a permanent figure, compared 

 with the spring, which in every part of 

 the vibration alters its distance from the 

 axis, and in every part of its length has a 

 different degree of rotatory motion, it 

 cannot be expected, nor does it happen, 

 that a balance, which is found to be in 

 poize, along .with its spring, when out of 

 the chronometer, will make equal vibra- 

 tion, as to time, in all positions when in 

 its place. And in addition to these diffi- 

 culties, there is one part of the arc of vi- 

 bration, where the force of the spring, 

 and the inertia of the balance, are not 

 simply in opposition to each other, but 

 are combined with the maintaining pow- 

 er: namely, during the action of escape. 

 The remedy for all these difficulties, 

 which is happily adopted in chronome- 

 ters for use at sea, is to place the axis in a 

 vertical position ; by which means the ba- 

 lance itself is not affected by gravity ; but 

 for pocket time-pieces, the ingenuity of 

 the artist is called upon for expedients, 

 of which it would be not easy to exhibit a 

 complete theory. The general principle 

 commonly used, and also adapted by Ar- 

 nold and Earnshaw, as tar as can be ga- 



VOL. VI. 



thered from the little they say in their 

 specifications to the commissioners of 

 longitude, is to consider the balance, 

 when out of adjustment for position, as a 

 pendulum weight above and below the 

 centre of suspension, acted upon by gra- 

 vity, and at the same time urged to a 

 quiescent point by the force of elasticity. 

 In these circumstances the vibrations will 

 be quickest when the point of stable equi- 

 librium is downwards, and they will be 

 slowest in the opposite position of the 

 machine. This leads to the remedy of 

 diminishing either the weight of the ra- 

 dius, or that side which is lowest when 

 the rate is most quick. Thus, if one of 

 the two adjusting screws, in fig. 7, were 

 downwards, in the position of quickest 

 rate, that screw would require to be 

 screwed a very little quantity inwards, 

 and the opposite screw to be screwed a 

 like quantity outwards, in order to reme- 

 dy this imperfection without much change 

 in the other adjustments And if a like 

 imperfection were found in the vibrations 

 of the balance, when tried in a vertical 

 position, having the lowest point at rest, 

 in a line at right angles to the line pass- 

 ing through the radn, a similar alteration 

 must be made in the expansion weights, 

 either by a careful flexure of the circular 

 arcs, or by altering the quantities of 

 those weights; or else by means of 

 small screws tapped into the weights 

 themselves, and directed towards the 

 centre, like the weights at the extremi- 

 ties of the radii. 



By these, and other correspondent 

 means, the balance may be made to keep 

 time, in all those positions wherein its 

 plane shall be perpendicular to that of the 

 horizon ; but even in these trials, very 

 great pains and labour may be required 

 to produce a high degree of accuracy ; 

 and in this course of operation, the skil- 

 ful workman may be under the necessity 

 of preparing a great number of expansion 

 weights and regulating screws, to be ap- 

 plied in trial, whenever the course of ad- 

 justment in one part shall carry him be- 

 yond the general conditions of the whole 

 machine. And after all, as the quantity 

 of action, in the spring, must alter the 

 quantity of pendulous effect, in this ctf- 

 rious and delicate time-measurer, it may 

 be doubted, whether the adjustments for 

 position in the vertical balance can be ef- 

 fectual any longer than while the arcs of 

 vibration continue permanent. This con- 

 sideration leads us to the necessity of an 

 adjustment in the maintaining power, in 

 order that the vibrations shall not fall off ; 



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