314 St. John — Wave lengths of Electricity on Iron Wires. 



off rapidly when the wires were lengthened or shortened from 

 either point. The result is shown graphically in fig. 2, where 



distances from Q are used as abscissas and deflections of the 

 galvanometer as ordinates. When the circuit is thus arranged, 



there is little effect pro- 



duced upon it by the 

 vibrator unless it is near 

 the point of resonance. 

 The period of the vibra- 

 tor is the controlling fac- 

 tor and the influence of 

 the secondary circuit is 

 greatly reduced. 



To determine the char- 

 acter of the vibrations 

 alongthe wire, the lengths 

 QP and RS, fig. la, 

 were fixed at S59 cm , the 

 exploring terminals were 

 moved along the rect- 

 angle and the bolometer 

 reading taken for each 

 position of the exploring terminals. The graphic representa- 

 tion of the results is given in fig. 1, of the plate where, as in 

 all the curves, the abscissas are the length of the sides of the 

 rectangle and the ordinates the bolometer readings. The char- 

 acter of the curve indicates a simple form of vibration. The 

 total length of the wire is equivalent to 7 half wave lengths. 

 The minimum points occur at nearly equal intervals, and the 

 distance from the minimum at T48 cm to the center of the 

 side QR may be taken as three half wave lengths. This fur- 

 nishes a ready means of calculating the half wave length. 



6o 



5 



40 



SO 



20 





800 



900 



