316 HENKY A. EOWLAND 



4-3 cm. Number of turns 3700 No. 20 B and 8 gauge single covered 

 cotton copper wire. Self -inductance as determined 5-30 henrys. 



BI B 2 . This coil was made by winding two wires in parallel and all 

 four of the terminals brought out to binding posts. Thus the coils 

 could be used as two single coils, when the coils will be denoted by the 

 symbols B^ and B 2 as the case may be, or as a single coil, the coils 5 1 

 and B 2 being joined up in series or in parallel. The dimensions of the 

 coils BI B 2 were the same as A. Each of the coils B^ and B 2 were 

 made up of 1600 turns of No. 22 B and 8 single covered cotton copper 

 wire. The self-inductance of these coils taken separately when com- 

 pared with P, which was determined absolutely, was nearly 1 henry. 

 On this account B was taken as being 1 henry, and the other coils were 

 compared with it as a standard. 



C. Same dimensions as P 2 . Number of turns 1747 of No. 22 B and 

 8 single covered cotton copper wire. Self-inductance as determined 

 1-30 henrys. 



Condensers. 2 and 3. Two paraffined paper condensers that had a 

 capacity of 2 and 3 microfarads respectively. 



Jd Troy. A -Jd microfarad standard mica condenser built by the 

 Troy Electric Co. 



Jd Elliott. A -Jd microfarad standard mica condenser built by Elliott 

 Bros. 



Resistances. The resistances used in the experiments were of two 

 kinds, those wound with double wire so as to have no self-inductance, 

 as the ordinary resistance box, and those wound on frames or cards 

 which had some small self-inductance, but almost no electrostatic 

 capacity. The resistances which had self-inductance are called open 

 resistances to distinguish them from resistance boxes, and were of 

 different kinds and dimensions. 



Sources of Error and Experimental Difficulties 



In all work with alternating currents there are two great sources of 

 error that have to be guarded against. These are the errors that may 

 arise from the inductance of one part of the apparatus on another, as, 

 for example, the direct induction of a coil in the circuit on the coils 

 of -the electrodynamometer, and the effect of the electrostatic capacity 

 of the leads and connections. In connecting the coils great care had 

 to be taken to avoid the effect of electrostatic action of the leads and 

 connections. For if there was a current of very considerable magni- 



