340 Mr. 0. A. Chant on the Variation of 



In PL VII. fig. 9 are shown readings and curves obtained 

 with the 20-cm. oscillator, with various lengths of wire, and 

 in fig. 10 are similar readings with the oscillator of double 

 the size, i. e. with 40-cm. plates : while in fig. 11 is shown a 

 series of three successive carves given by the 20-cm. oscillator 

 with the same length of wire. These illustrate the method 

 moderately well. 



Remarks on the Table ami the Carves. 



A glance at the table will show that the oscillators used 

 can be divided into two distinct groups, the first including 

 the four smaller ones, and the second the three larger ones, 

 while the oscillator with 30-cm. plates lies between the two 

 groups. The results with each group are consistent amongst 

 themselve>, while the 30-cm. oscillator behaved in a very 

 irregular manner. 



For the first group (the smaller ones) the positions of the 

 minima for any particular length of wire are independent of 

 the size of the oscillator, i. e. they depend only on the wire's 

 length. In this case the oscillator does not force its period 

 on the wire. 



In the second group, on the other hand, the positions of 

 the minima depend only on the size of the oscillator, not at 

 all on the length of the wire. 



The conclusion seems natural that, in this latter case, the 

 distance of the minimum from the free end is one quarter of 

 the wave-length of the oscillating system. The values of this 

 quarter-wave-length deduced from the table are : — 



For 35-cm. oscillator... 132" 7 cms. (mean of 11 results). 



- 40 117-1 ., ( ., 21 „ ). 



„ 50 „ ... 171-5 „ ( „ 6 „ ). 



Now it is possible that the proximity of the wire to the 

 oscillator may have the effect of virtually increasing the size 

 of the oscillator, and if such is the case all the quarter-wave- 

 lengths so determined are too great. According to Poincare'- * 

 deduction from the homogeneity of the fundamental equations, 

 the wave-length of an oscillator or resonator varies directlv 

 with its linear dimensions. In fig. 12 the points A, B, C have 

 abscissae proportional to the dimensions of the three larger 

 oscillators and ordinates proportional to the quarter-wave- 

 lengths given above. It is seen that they lie very approxi- 

 mately on a straight line, but this line does not pass through 

 the origin. Let us now draw a line parallel to it and passing 



* Poincare, Les Oscillations JSlectriques, Art. 53. 



