56 



CONSTRUCTION OF THE APPARATUS. 



firmly in the lead the form shown in fig. 46 is given to the wire. 

 The l& r and friction weights are cut out of a thin brass plate, the 

 four-gramme weight out of a sheet of zinc. The form shown in 

 r and u (fig. 43) is given to these weights in the following manner: 

 The weights are placed upon a piece of lead, and by means of a 

 punch (fig. 47), a hole is punched in the middle of each; two 

 parallel cuts are now made from the side to the hole, the whole 

 hammered flat, and accurately adjusted to the proper weight by 

 filing. Thin sheets of metal may be cut by a pair of common strong 



FIG. 46 (real size). 



FIG. 47 (\ real size}. 



scissors, but it is better to use for the purpose a pair of smal 

 shears, of which one jaw is clamped horizontally between a 

 A small vice is indispensable, at least one of the kind represented 

 fig. 48, but much more servicable is the parallel vice (fig. 49^ 

 The vice is secured to the corner of a very firm table or bench by 

 the screw a ; the handle d is used for turning the screw c, and 

 clamping any objects between the cheeks 5 5. 



The upper part of the vice may be loosened by turning the 

 winged screw e, and clamped again in any required position ; this 

 is very convenient for many purposes, and almost indispensable if 

 the vice cannot be attached to a corner which is perfectly accessible 

 all round. The small anvil carries projecting ' horns ' for hammer- 

 ing wires or plates of metal either round or into angles. 



The cord should be of twisted silk, and so long that one weight 

 is close to the wheel when the other touches the floor. In 



