OF ARTS AND SCIENCES. 



235 



cases we employed an experimental receiver like that used in the 

 earlier studies referred to. The core was a bar of Norway iron, 

 I inch in diameter and 8 inches long, wound with 2,750 turns of No. 18 

 (B. «&; S.) insulated copper wire. The current which traversed these 

 coils was furnished by a dynamo machine. It passed through an in- 

 candescent lamp and a variable resistance frame, with which last the 

 magnet was placed in derived circuit. By varying this current any 

 desired strength of field could be obtained. In all our experiments 

 the core of the electro-magnet was far removed from saturation, so that 

 we may assume the strength of its field to have been proportional to the 

 curi'ent traversing its coils. The strength of this current was measured 



/OO £00 JOQ 'too 



in the earlier experiments by a Thomson graded galvanometer, and in 

 the later ones by a AVeston milliamperemeter. The transmitter current 

 was furnished by a single storage cell, and the organ-pipe which served 

 as a source of sound was placed in a distant room. The arrangement 

 of the stroboscopic fork was similar to that used in the previous work. 

 The first measurements were made with an ordinary magneto-tele- 

 phone as a receiver. The line current was varied, and the correspond- 

 ing excursion of the diaphragm determined, with the results given in 

 Table I. Series C is graphically illustrated in Figure 1. The values 

 given in the table are the mean of three or more closely concordant 

 readings. In this and the following tables the current is given in 

 milliamperes, the excursion in terms of one micrometer division as a 

 unit. In the figures the abscissas represent currents, and the ordinates 

 excursions. 



