346 On the Construction and 



below the centre, and they must be raised slightly until 

 the vibrations of the beam do not change in rapidity on 

 loading. 



The next thing is to equalize the length of the arms of the 

 beam. To do this, the scale pans with the weights in them 

 and stirrups to which they are hooked are removed and 

 changed. The end of the beam which now preponderates is 

 the longest, and the points of that end are to be moved by 

 the adjusting screw nearer to the centre, or what is the same 

 thing, the opposite end of the beam is to be lengthened in 

 the same manner. The beam is then again to be brought to the 

 horizontal position by altering the weights in each pan, and 

 the scale pans are to be shifted again and again, until the 

 horizontal position of the beam is no longer affected by the 

 change. 



This is a most tedious and difficult operation ; a whole 

 day^s incessant work being sometimes necessary. 



Should the double points which bear the scale pan stirrup 

 not be exactly equidistant from each other at both ends, the 

 stirrups will not fit if changed ; in this case the operation for 

 adjusting the length of the arms must be modified thus : — 

 The beam with the empty scale pans is to be brought hori- 

 zc ntal by putting small weights in the pans, and then a one 

 thousand or two thousand grain weight is to be placed in each 

 pan, and if the arms are not equal, the longest will pre- 

 ponderate ; the large weights are then to be removed, the 

 length of the arm shortened by the adjusting screw, and the 

 beam with the empty pans again brought to the horizontal 

 position ; the large weights are again to be put in, and this 

 is to be repeated until the beam still remains horizontal after 

 the large weights have been added. 



The next thing is to equalize the weight of the scale pans, 

 which is to be done by filing carefully a small portion off the 

 one which preponderates, when the empty pans are hung to 

 the beam as adjusted. 



