I 1835.] Balances for Delicate Weighing 91 



! was the heaviest was adjusted by thrusting the point bj' 

 means of the before mentioned screws nearer to the centre 

 of the beam. When it was correct or very nearly correct 

 I took off the scale pans and reversed them by placing them 

 on the opposite ends of the beam, and on trying them in 



1 this position I found they gave the same indication, which 

 was a proof that the two scale pans and weights were equal^ 

 and one not heavier than the other. After a whole day's 

 trial however I found I could not adjust to perfect accuracy 

 and so I left the balance out of equipoise about YoW^h of 

 a grain in 100 grains. This error is equal to the 50,000th 

 part of the weight which is quite accurate enough for even 

 delicate purposes, but the error being known it is obvious 

 that subtraction or addition is all that is required in order 

 to arrive at a perfectly correct result should a greater degree 

 of accuracy be required. 



13. Figure 8 represents my third balance which is 

 adapted to weighing quantities from 100 to 2000 grains o 

 Though not so sensible in its indications as the last describ- 

 ed balance, it is fully adequate to most experimented pur- 

 poses falling within the weights just specified. Its sensi- 

 bility at first was very great but having been in considera- 

 ble use its delicacy of indication has become considerably 

 diminished; ^^odths or the 50th part of a grain however, 

 still gives a decided result with 2,000 grains in each scale 

 which is equal to the TooWodth part of the weight. Sir 

 M. Farraday in his chemical manipulation tells us that a 

 balance is an exceedingly good one if it indicates to the 50 

 or 60 thousandth part of the weight. 



14. It will be perceived by Fig. 8, that the central por- 

 tion of this balance which is represented of the real size, is 

 exactly similar to the last. It requires therefore no descrip- 

 tion, the former description in Para. 10, will answer for both. 

 The means of adjustment, hov/ever, and the bearing points 

 are different. The balance is equipoised before using it, not 

 by a small moveable wire as g, figure 2, but by means of a 

 small ball a, screwing along the wire b, b, figures 9 and 

 10 :-=-and the bearing or suspending points at each end of 

 the beam are double. Fig. 9, is a plan, and figure 10 



a front view of the manner in which the points are fix- 



