130 Prof. C. V. Raman and Mr. Ashutosh Dey on the 



resonance, are of the same form as those described by 

 Klinkert in a paper on electrically-maintained vibrations *. 

 It is noticed, however, that when the tension is such that 

 the wire vibrates in two, three, or larger number of segments, 

 and the electromagnet is not too far away from the wire, 

 the motion of the usual type first set up is unstable, and 

 gradually changes form, the nodes ceasing to be points of 

 rest, and the frequency of vibration changes to a value 

 which is a submultiple of the frequency of the fork. For 

 instance, if the wire initially divides up into two segments 

 and vibrates with a frequency of 60, its centre, which at 

 first is a node, gradually acquires a very considerable motion, 

 and the frequency of the vibration alters to 30. Similarly, 

 if the wire initially vibrates in 3 segments, the frequency 

 changes to 20 when the instability sets in ; when the initial 

 vibration is in 4 segments, the frequency changes to either 

 30 or 15 according as the instability does or does not result 

 in a movement of the centre of the wire, and so on. 



The rate at which the instability sets in and results in a 

 change of type depends upon the position of the electro- 

 magnet, its distance from the wire, and the strength of the 

 intermittent current which excites it. Generally speaking, 

 the rate of increase of the motion at the nodes is small, and 

 it may take some minutes for the change to develop to the 

 fullest extent. The gradual alteration of the form of 

 the vibration may thus be closely studied, and this fact adds 

 considerably to the interest of the experiment from the 

 acoustical point of view. If the distance of the electro- 

 magnet from the wire and the strength of the exciting 

 current be suitably proportioned, the vibration with the 

 altered frequency finally reaches a steady state, the ampli- 

 tude of variation then attaining its maximum. If, however, 

 the electromagnet be too near the wire, or if the exciting- 

 current be too strong in proportion to the distance, the 

 motion continues to increase in amplitude till the wire 

 finally comes up against the pole of the magnet. This 

 occurs most frequently when the tension is small and the 

 wire divides up initially into a considerable number of 

 segments. 



To enable the frequency of the field to be compared with 

 that of the motion set up by it, the vibration-curves of some 

 selected point on the wire and of a small style attached to 



* G. Klinkert, Annalen dor Vhysik, vol. lxv. (1898). For a practical 

 application, in acoustics, of this class of vibration, see 'Science A bstracts' 

 (1916), p. 433. 



