Management of delicate Balances. 349 



the other. The weight having been removed, the substance 

 to be weighed is substituted, and the supplement of the 

 weight is made up by adding weights, from which the weight 

 required is easily known by a single operation. The adjust- 

 ment of the points of suspension to the line of the centre of 

 motion, is a very tiresome operation, as it must be done by 

 screwing up and down the adjusting screws, in which great 

 nicety is necessary, because half a turn of the screws will 

 cause a very considerable alteration, and it is also necessary 

 to take out the beam and remove the scale pans each time 

 that the screws require alteration. 



In adjusting a beam for " supplementary weighing/' this is 

 avoided altogether by using a heavy adjusting ball and a long 

 screw upon the centre of the beam, instead of the minute 

 one generally used; and the beam when loaded having been 

 made to vibrate slowly by screwing up the points of suspen- 

 sion, the adjustment is readily completed by screwing up the 

 adjusting ball, so as to raise the centre of gravity of the beam 

 until the moment of the force of its gravity becomes as near- 

 ly as possible a very little less than the difference of the 

 moments of the forces acting upon the arms. 



This is practically a very great convenience, as it is not 

 necessary to remove the beam to make the adjustment, which 

 can be done readily by hand while the beam is in its place. 



In the balance, as commonly adjusted, this cannot be done, 

 because the beam would upset when the heavy load was 

 removed, and lightened weights substituted. 



As the counterpoise weight for supplementary weighing is 

 constant, I have made use of a further alteration, by applying 

 a fixed counterpoise, or f bob' to the end of the beam, so that 

 its centre of gravity occupies the exact place of the point of 

 suspension of the scale pan, by which method one scale pan 

 is sufficient, and there being only two bearings instead of 

 three, the friction which impedes the motion of the beam, 



and thereby decreases its sensibility, is reduced to two-thirds. 



2 Y 



