1878.] 



using the Balance with great delicacy, §c. 



7 



arch which fits on to the beam, as shown in the end view (fig. II, 2). In 

 each of these sides are cut two V-shaped notches directly opposite to 

 each other, one of the opposite pairs being 6'654 milling, (about J inch) 

 distant from the other pair. Two equal riders of the shape shown in 

 fig. II, 3, are placed across the bridge, and are of such a size that they 

 will just fit into the bottom of the notches. When one of these rests 

 across the bridge the other is raised up from it. The lowering of one 

 rider and the raising of the other corresponds herefore to a trans- 

 ference of a single rider from one pair of notches to the other. The 

 length of the half beam being 202" 716 millims. and the distance 

 between the notches 6*654 millims., this transference will be equivalent 

 to the addition to one pair of 3 '03 284 of the weight of the rider used. 

 As I have generally used a centigramme rider this means 0'3284 

 mgms. 



Two levers IV (fig. II, 4), with hooks hti are used to raise one rider 

 while the other is lowered. These levers are worked by two cams cc 

 on a rod R, which is prolonged out of the balance case to the observer. 

 By turning this rod round, the one lever is raised while the other 

 is depressed. The hook at the end of the raised lever picks up its 

 rider while the other hook deposits its rider on the bridge, and then 

 sinks down between the raised sides (as shown in fig. II, 4), leaving 

 the rider resting freely on the bridge. 



The levers are so adjusted that the beam even in its greatest oscil- 

 lations never comes in contact with the hooks. 



This arrangement might probably be still further perfected by intro- 

 ducing two small frames for the riders to rest upon, the frames resting on 

 the beam by knife edges. It would then be certain that the movement 

 of the riders was equivalent to a transference from one knife edge to 

 the other, whereas the rider at present may not rest exactly over the 

 centre of the notch. But I find that I get fairly consistent results by 

 lowering the rider somewhat suddenly so as to give it sufficient 

 impetus to go to the bottom of the notch, and have not therefore 

 thought it necessary as yet to introduce more complicated apparatus. 



In place of the right hand pan of the usual shape, another of the 

 shape shown in fig. Ill, 1, is employed. To the centre of the pan un- 

 derneath is attached a vertical brass rod which passes downwards 

 through the bottom of the inner case of the balance. To the under 

 side of this case is attached the clamping arrangement before referred 

 to. This consists of two sliding pieces (fig. IV, l r ss) working hori- 

 zontally in a slot cut in a thick brass plate which is fastened to the 

 case. Through a circular aperture in this plate (the slot is not cut 

 through the whole thickness of the plate, but only as shown in 

 fig. IV, 2) and about the middle of the slot hangs the rod r attached to 

 the scale pan. 



By means of right and left handed screw on a rod R, which is pro- 



