﻿of Electricity on Iron Wires, 



429 



point was passed. The wires were renewed, and the operation 

 repeated again and again. A sharp and unmistakable maxi- 

 mum was found when P Q was 859 centim. long. (fig. 3). The 

 effect fell off rapidly either when the wires were lengthened or 

 shortened from this point. The result is shown graphically in 

 fig. 2 (PI. XII.), where distances from Q are used as abscissas 

 and deflexions of the galvanometer as ordinates. When the 



Fig. 3. 



800 



900 



circuit is thus arranged, there is little effect produced upon it 

 by the vibrator unless it is near the point of resonance. The 

 period of the vibrator is the controlling factor, and the in- 

 fluence of the secondary circuit is greatly reduced. 



To determine the character of the vibration along the wire, 

 the lengths Q P and R S (fig. 1) were fixed at 859 centim., 

 the exploring terminals were moved along the rectangle, and 

 the bolometer-readings taken for each position of the explor- 

 ing terminals. The graphic representation of the results is 

 given in fig. 1 of PI. XII., where, as in all the curves, the 

 abscissas are the length of the sides of the rectangle and the 

 ordinates the bolometer-readings. The character of the curvo 

 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 748 centim. to the centre (fig. 1) of 

 the side Q R may be taken as 3 half wave-lengths. This 

 furnishes a ready means of calculating the half wave-length. 



