286 Mr. P. E. Shaw on some 



S as will give the required frequency, and finally adjust to 

 a maximum by the iron core in 2 (see expression I.). 



This frequency (400 was used) must be an exact multiple 

 of that of the fork (100), then between each charge received 

 by S from the fork, there would be four complete surgings 

 between S, C l5 2 ; the potential changes would be con- 

 siderable, and violent shocks might be obtained. 



L may be varied by the introduction of any number of 

 coils at C 2j or by moving a core of iron wires in C 2 . This 

 latter is a convenient adjustment, but wasteful on account of 

 hysteresis. The adjustments are (I) the mercury-contact 

 (M.C.), (2) the rheostat, (3) adjustable L in C 2 . Place 

 one ear on the flat condenser (taking care to avoid getting a 

 shock from its terminals), listen to the note heard in it, and 

 change (1), (2), and (3) up to maximum loudness. The 

 adjustment (1) must on no account be neglected ; the method 

 adopted was to have the fork rigidly held, but capable of 

 being rotated by any small amount in a vertical plane. 



Thus, as above described, we have a circuit with a given 

 frequency, whose note can be raised to a maximum intensity. 



Now turn to the secondary (or receiving) circuit (fig. 2). 



!=C 



The coil C 3 is placed parallel to C 1? and catches the waves from 

 it ; C 4 is an auxiliary coil. The condenser S is in series in 

 the circuit, and not, as in the primary, shunted across the 

 ends of the coils. There are two other coils in the same 

 circuit: — (1) Mj is the coil of the relay, with its microphone- 

 carbons shown above it ; (2) the small resistance-winding o£ 

 a telephone induction-coil, the large resistance-winding 

 being in series with the telephone T. 



If now the coil C 3 is taking up the waves from the sending- 

 circuit, and the variables C 4 and S are set for exact tuning 

 (to frequency 400) a note of maximum loudness will be heard 

 in the telephone T. In the primary it is convenient, though 

 wasteful, to have an iron core in a coil for the small adjustment 

 of L, but in the secondary it would be useless, since /* is small 

 for the very weak currents existing. 



