320 St. John — Wave lengths of Electricity on Iron Wires. 



long. The additions of wire for the successive maxima after 

 the first were 261, 256-5 and 255*5. These should be half 

 wave lengths. The last two agree well, but the first differs 

 from the average of the last two (256 cm ) by 5 cm . The sides 

 were fixed at 818 cm , and the wave form tig. 3, of plate was 

 obtained, from this the half wave length was found to be 

 255*6 cm , and the total length of the circuit 7 half wave lengths. 

 By fixing the sides of the rectangle at 562'5 cm and 306 cm a 

 similar investigation showed the circuits to be respectively 

 5 and 3 half wave lengths long. 



An explanation of the fact that the distance between the 

 first and second maxima was anomalously large may possibly 

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

 but 45 cm long, so that the effect of the closed end was relatively 

 great 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. Besides in the 

 first case the capacity was largely local, while in the others it 

 was mainly distributive. This same effect appeared in every 

 case and seemed a constant phenomenon. 



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 cm long, and the end capacities 

 equivalent to 62 cm of wire. The half wave length was 30 + 

 127-5x2+62x2=409 cm . 409-^255-6 = 1-6 nearly. This was 

 the only indication observed of the complexity in the vibra- 

 tion of the oscillator. It appears that when the oscillation is 

 particularly active it can excite a circuit having this ratio to 

 itself, or that the vibration is not a simple one. Sufficient 

 time was not at my disposal to decide this point which is left 

 for future investigation. 



An annealed iron wire (diameter 0*1186 cm ) was put in 

 place of the copper and the same series of observations re- 

 peated. The results are shown in the lower curve of the upper 

 pair in fig. 4 of the plate. The maxima E, F, G, H, appear at 

 42'5, 301, 553 and 805 cm : in each case before the correspond- 

 ing maxima with the copper, and the difference is seen to in- 

 crease with the length of the circuits. The successive additions 

 were 258'5, 252, and 282 cm . The last two agreeing, but the 

 first as with the copper is much larger. With the sides of the 

 rectangle fixed at 805 cm , the form of the wave was found as 

 shown in fig. 2 of the plate. The third minima occurs at 

 740 cm . Calculated as before the half wave length is 740 + 15 

 = 756, 755-^3=251-6 cm . This agrees well with the value 



