ST. JOHN. WAVE LENGTHS OP ELECTRICITY. 239 



series were retained. The results here given rest upon such 

 readings. 



An examination of the curve shows four maxima, E, F, G, H, 

 occurring when the sides of the rectangle were 45, 306, 562.5, and 

 818 cm. long. The additions of wire for the successive maxima 

 after the first were 261, 256.5, and 255.5 cm. These additions should 

 be a half wave length ; the last two are nearly the same, but the first 

 differs by 5 cm. from the average of the last two, which is 256 cm. 

 With the sides fixed 818 cm. long, the wave form along the circuit 

 was determined by sliding the exploring terminals over the wires by 

 short steps, and observing the bolometer throws for each position. 

 The result is shown in Figure 3 of the Plate. The critical points 

 were determined several times, and a method similar to that described 

 above was used to assure the constant activity of the spark. The 

 curve shows three minima, occurring at 240, 496, and 752 cm. 

 Starting from the point O these give half wave lengths of 255, 256, 

 and 256 cm., with an average of 255.6 cm. The third minimum at 

 752 was determined with care, as it was to be used as a basis for 

 calculating the half wave length. A small error in determining the 

 position of this miniumm would be divided by 3 in obtaining the 

 result, since its distance from O was 3 half wave lengths. The total 

 length of the circuit was 7 half wave lengths. From the third min- 

 imum to the end it was one fourth of a wave length, the capacities 

 bring each equivalent to 62 cm. of the wire. By fixing the length 

 of the rectangle at 562.5 and 306, a similar investigation showed the 

 circuits to be respectively 5 and 3 half wave lengths long. 



An explanation of the fact mentioned above, that the distance 

 between the first and second maxima was anomalously large, may 

 possibly be this : the sides of the rectangle for the first maximum 

 were but 45 cm. long, so that the effect of the closed end in increas- 

 ing the self-induction was relatively large, and the maximum appeared 

 earlier than it otherwise would ; but when the rectangle was 300 cm. 

 long, the influence of the closed end became relatively small, and 

 the second and future maxima came in the normal positions. In 

 the first case the capacity was mostly local, while in the second it was 

 largely distributed, and the length of the circuit was greater than 

 the wave length. This same effect appeared in every case, and seemed 

 to be a constant phenomenon. 



The maximum I, omitted from the above discussion, was not con- 

 stantly present, but appeared when the primary spark was particularly 

 active, and seemed to belong to a circuit whose period was to the 



