A NEW CURRENT WEIGHER, ETC. 



501 



other ; in any one division the 80 strands lie in two parallel layers, the system being 

 formed by winding a continuous length of silver wire over two brass rods cut with a 

 screw thread of ^g-inch pitch ; no two strands are in contact. After the completion 

 of the winding the silver wires were soldered to the rods by running a very soft 



Fig. 17. 



Leads and commutator for suspended coil, a shows diagrammatic plan of commutator 



(looking upwards). 



fusible metal into the V-grooves. The length of a strand is 10'5 centims., but the 

 distance between the rods is a little less than this. Fig. 17 illustrates the manner in 

 which a set of silver wires is placed in position. Before their insertion the sensitive- 

 ness of the balance was such that an added load of 1 milligramme produced a 

 deflection of 0'9 scale division ; afterwards the corresponding deflection was 0'85 

 scale division, a diminution in sensitiveness of 6 per cent. only. The concentric 

 cable attached to B' is clamped to the main pillar of the balance, and passes through 

 a hole drilled in the base of the balance table to the multiple commutator and plug 

 board described on p. 521. 



The first setting of the coils on the tables of the balance involved the following 

 operations : 



(a) Levelling of one suspended cylinder by adjustment of the lengths of the 

 suspension wires and of the masses on the limbs of the spider. 

 (6) Levelling of the concentric fixed cylinder. 



(c) Approximate setting of the fixed cylinder, so that the mean diametral plane of 

 all the coils on it coincided with the mean diametral plane of the suspended coils. 



(d) Levelling and vertical adjustment of the other fixed cylinder until its mean 

 diametral plane coincided with the corresponding plane of the first fixed cylinder. 



(e) Levelling and adjustment in vertical height of suspended cylinder No. 2 in 

 order that conditions (a) and (c) should hold with it. 



(/) Setting of each pair of cylinders to be concentric. 



