94 On a Proposed New Method of Weighing, 



weight : for example, when the real weight of the rider is 

 ~ of a grain the subdivisions of the index scale should 

 represent -^th part of the rider weight, or -001 of a grain. 



The beam should be constructed as simply and of as few 

 pieces of metal as possible ; the fixed constituent members 

 of the beam should be fastened together as firmly as possible ; 

 the movable pieces, the ball and tongue, should be fitted to 

 move neither too stiffly nor too loosely, but so as to retain 

 whatever position they are placed in during the adjustment 

 and after-use of the beam. 



When the skilled workman has exerted the utmost care 

 and ability in making such a balance-beam, the instrument 

 will require adjustment of the tongue and ball, that is to 

 say, of the centre of gravity of the beam, so as to suit it for 

 the special work for which it is to be used, whether for 

 quantity of work or for extreme accuracy regardless of the 

 quantity of work performed in a given time. When this 

 adjustment has been effected, it is probable that the index 

 readings on the scale will be found to deviate more or less 

 from the required decimal subdivisions of the rider weight. 



A few sentences will elucidate the details of this final 

 adj ustment of the beam. By screwing up the ball, over the 

 centre of the beam, we bring about two results : — 



1. We raise the centre of gravity of the beam ; and 2. 

 As the ball is at best only an approximation to a 

 true and uniformly dense sphere revolving on a vertical 

 axis, by its revolution we displace, in some degree, the centre 

 of gravity, in a direction other than the vertical. After 

 screwing up or lowering the ball, the balance of the arms of 

 the beam is found to be disturbed, and it becomes necessary 

 to restore equilibrium by adjustment of the tongue. The 

 tongue should be movable in azimuth on a plain cylindrical 

 pin, without rising or falling on a screw-thread. 



We may raise the ball until the balance becomes unstable, 

 or we may lower the ball and consequently lower the centre 

 of gravity of the beam until stability (disturbed by raising 

 the ball) is fully restored. But when we require the greatest 

 sensibility consistent with stability, we must, by a series of 

 trials, bring the centre of gravity to a position a very little 

 below the point upon which the beam oscillates (the centre 

 knife-edge). 



In the practice of this latter adjustment it will greatly 

 assist operations to paint a small neat black dot on the 

 equator of the ball, so as to be able by means of this mark 



