248 Prof. E. Taylor Jones on a 



All the bridge resistances were compared with the N alder 

 box corrected for temperature. The result obtained for the 

 self-inductance of A was 70'15xl0 9 cm. The same method 

 was employed for the self-inductance of the coil B, the 

 result being '0112 x 10 9 cm. 



The mutual inductance of the coils A and B was compared 

 with that of a standard solenoid and secondary coil. The coil 

 B and the secondary wound on the solenoid were connected in 

 circuit with a ballistic galvanometer, and the swings observed 

 produced by reversing measured currents in A and in the 

 solenoid. The result was M = *319 x 10 9 cm. 



(7) r Llie Capacity of the Coil A and of the Electrometer. 



As far as could be observed from a partial dissection of the 

 coil A, it consists of 100 probably conical layers of No. 36 

 silk-covered copper wire, each separated from the next by 

 three or four disks of paraffined paper. The coil may there- 

 fore be regarded as forming 99 parallel plate condensers, but 

 as each layer (except the two end ones) acts as negative 

 plate to the layer above it and positive plate to the one below 

 it, the internal windings will not on the whole absorb much 

 charge. The effect on the period of electrical oscillation of 

 the capacity of one layer on the next was calculated by Lodge 

 and Glazebrook for the coils used by them in their experi- 

 ments on the determination of " v" *. 



The result given is that the capacity of the condenser in 

 circuit with the coil is to be divided by 



n-2 C 

 1_ n 2 "C 



where C is the capacity of the condenser, C the capacity of 

 one layer of the coil on the next, and n the number of layers. 

 This result was assumed to apply to the present case, and 

 (J' was determined by finding one of the wires connecting 

 two consecutive layers near the middle of the coil, breaking 

 this, and comparing the capacity of the condenser so formed 

 with that of condenser I. This was done by a method in 

 which the electrical tuning-fork was used to connect one-half 

 of the coil (or the inner plate of the condenser) alternately 

 to a battery of 18 storage-cells and to a galvanometer. One 

 pole of the battery, one terminal of the galvanometer, and 

 the other half of the coil were earthed. By means of a well- 

 insulated switch either the coil or the condenser could be 



* Lodge and Glazebrook, Oamb. Phil. Soc. Stokes Commemoration 

 (1899), p. 171. 



