﻿436 Mr. C. E. St. John on Wave-lengths 



The maximum I omitted from the above discussion was not 

 constantly present, but appeared when the primary spark was 

 especially active, and seems to belong to a circuit whose 

 period is to the period of the vibrator in the ratio of 5:3. 

 The sides of the rectangle were 127-5 centim. long and the 

 end capacities equivalent to 62 centim. of wire. The half 

 wave-length was 30 + 127*5 X 2 + 62 x 2 = 409 centim. 

 409 -T- 255-6 = 1-6 nearly. 



This was the only indication of complexity in the vibration 

 of the Hertz vibrator; and it may. be explained by supposing 

 that such a vibration is superposed upon the fundamental rate 

 of the oscillator, or that the oscillator when particularly active 

 can excite a circuit having such a ratio to itself. This last 

 seems the simpler, but it is difficult to see why a circuit of 

 the ratio 3 : 2 should not be excited as well. The maximum 

 I would indicate the presence of an undertone rather than an 

 overtone. This point requires more investigation than it 

 has been possible to give it, and will be left undecided for 

 the present. 



An annealed iron wire (diameter 0*1186 centim.) was put 

 in place of the copper, and the same series of observations 

 repeated. The results are shown in the lower curve of the 

 upper pair in fig. 4, PI. XII. The maxima EFGH 

 appear at 42*5, 301, 553, and 805 centim., in each case 

 before the corresponding maximum with the copper; and the 

 difference is seen to increase with the length of the circuits. 

 The successive additions were 258*5, 252, and 252 centim., 

 the last two agreeing, but the first, as with the copper, is much 

 larger. With the sides of the rectangle fixed at 805 centim., 

 the form of the wave was found as shown in fig. 2 of the 

 plate. The third minimum occurs at 740 centim. Calculated 

 as before, the half wave-length is 740 + 15 = 755. 755-T-3 

 = 251*6 centim. This agrees well with the value 252 given 

 above by the last two additions, but differs by 4 centim. from 

 the value found when the copper was used. 



The same series of observations was repeated with a second 

 pair of finer wires (diameter of copper wire 0*07836 centim., 

 diameter of iron wire 0*0785 centim.). The results are shown 

 in the lower pair of curves in fig. 4 of the plate. A com- 

 parison of the curves shows the same general result, which 

 appears more distinctly from the following table : — 



