BALANCED MAGNET CHRONOSCOPES 455 



of the stimulus branch of the clutch circuit may be arranged 

 with a precise interval between. In other cases, a simple relay 

 of low resistance and inductance has been employed with no 

 appreciable error resulting, the unbalancing of the two branches 

 being slight. In general, the use of a simple relay is not safe, 

 and hence the balanced relay shown in figure 1 has been developed. 

 As shown in the diagram, the closure of the master key will 

 automatically set the armature lever of the relay against the 

 stop on the side of magnet 3-4, and when the master key is 

 completely closed, current will flow equally through this magnet 

 and through magnet 1-2 : and since these magnets are duplicates, 

 and one is in the circuit of each of the clutch magnets, the two 

 branches of the circuit are perfectly balanced. On depressing 

 the stimulus key, contact is made between 1 and 2 (of the stimulus 

 key), thus giving the stimulus, at the same moment that contact 

 is broken between 2 and 3, interrupting the circuit through the 

 anterior chronoscope magnet. The armature lever of the relay 

 being released from magnet 3-4, moves over to the opposite 

 stop, and recompletes the circuit through the anterior clutch 

 magnet, through the third relay magnet, thus again balancing 

 the circuits, and assuring also that the armature lever of the 

 relay will be held in the new position even after the current 

 through magnet 1-2 is interrupted by the movement of the 

 reactor. In the diagram, the pneumatic reaction key which has 

 been found most reliable, is shown, without the rubber bulb 

 which the reactor squeezes. The stimuli are schematically shown 

 as flashes of two low- wattage mazda lamps, either one being 

 switched in before the measurement. For discrimination, lamps 

 of two colors might be used, enclosed both in the same box with 

 a milk glass window, so that the color would always appear in 

 the same place. 



In the set-up of figure 1 both master key and stimulus key 

 must be held down from the time each is pressed until the end 

 of the registration. The balanced relay is self-setting, so that 

 the actual procedure is simple. The tune of action of the relay 

 must be well inside of the reaction limit, and must be over 15 

 sigma, in order to allow leeway for the chronoscope clutch. 



