BALANCED MAGNET CHRONOSCOPES 453 



This requirement is to be borne in mind in connection with the 

 details which follow. 



For the set-up in figure 2, with voice keys 3 for the association 

 reaction, storage cells connected in series to give over four volts 

 will operate the clutch. The higher voltage with resistance, as 

 in figure 1, is more desirable. In the arrangement shown in 

 figure 1, a voltage-reducing lamp-board is used, with one 100 

 watt lamp and one 60 watt lamp in the primary (left-hand) 

 pair of receptacles, and two 100 watt lamps in the secondary 

 (right-hand) pair. With this arrangement the total current in 

 the two branches of the clutch circuit, the master key being 

 completely closed, is approximately 0.6 ampere. 



The current is divided through the two branches of the circuit 

 through the master key (refer to figure 2 : figure 1 is more compli- 

 cated), which, as will be noticed, completes the circuit through 

 the anterior magnet (the non-rotating magnet) a moment before 

 completing the circuit through the posterior (rotating) magnet 

 in the other branch. This is necessary in order that the clutch 

 shall always be locked in the non-rotating position when the 

 key is pressed. The master key is a two-contact key of new 

 design, involving three strips of spring brass, or better, or phos- 

 phor bronze, so arranged as to be self-scouring, and therefore 

 needing no gold contacts. When the master key is released, 

 current is "off" both branches of the clutch circuit, thus permit- 

 ting resetting of the register hand, and making the clutch 

 circuit perfectly safe. 



OPERATION IN THE ASSOCIATION REACTION 



The set-up of figure 2 has now been completely described, 

 with indication of alternatives in both motor circuit and clutch 

 circuit. The method of operation will now be described before 

 proceeding to the more complicated set up of figure 1. 



Operator and reactor being in position before their respective 



8 For description of the voice key, see Psychological Review, 1913, xx, 250-253. 

 The Ewald chronoscope described there as satisfactory proved later very unsatis- 

 factory, it got out of adjustment and could not be put in repair again. 



