J. Trowbridge — Electrical Waves on Iron Wires. 309 



electric strains and deformations. I could not detect, however, 

 such effects. I was dealing with single discharges, not repeated 

 ones, such as are employed in obtaining wave lengths along 

 wires, and the photographs of such single discharges showed 

 no evidence of inconstancy in the capacity of my condensers. 

 If there was any effect of electrical hysteresis it affected both 

 my time circuit and my trial circuit alike. 



As an example of the degree of accuracy that can be 

 obtained in the measurement of the distances between the 

 oscillations on the negatives, the following table is given. The 

 distances between different numbers of oscillations is given in 

 the first column and the average length of the oscillation is 

 given in the third column. 



Distance in mm. Number of Average length 



between the first oscillations included of oscillations 

 and last oscillation. in this distance. in mm. 



22 -5 6 3-75 



26-1 1 3-73 



30- 8 3^4 



15-1 4 3-77 



Repeated measures between the same number of oscillations 

 give closer measures ; but one is apt to set the measuring 

 instrument each time on the same points on the negative. It 

 is evident that measuring each time the space between a differ- 

 ent number of oscillations gives the fairest result. It is sur- 

 prising how close one can set the measuring instrument upon 

 the serrations of the negative. 



It will be noticed below that the ratio between any two deter- 

 minations of the time on the time circuit is the same as that be- 

 tween the corresponding times on the trial circuits. When iron 

 wire of suitable diameter, however, was substituted for copper 

 wire of the same diameter and same geometrical form, in the 

 trial circuit, the ratio of the determinations of time in the time 

 circuit and the ratio of the oscillations on the iron circuit were 

 no longer constant. This inconstancy I desire to dwell upon 

 as my strongest proof that the period of electrical oscillations 

 on iron wires is not the same as that of oscillations on copper 

 wire of the same geometrical form. 



The arrangement of a suitable iron circuit gave me consider- 

 able trouble. The problem was to obtain a sufficient length of 

 iron wire to show any effect of change in periodicity and also 

 to obtain a sufficient amount of self-induction in order that the 

 distances between the oscillations on the photographs should be 

 measureable. The strong damping effect of iron did not per- 

 mit of my using more than four or five meters of wire. It was 

 not a simple matter to arrange two circuits, one of iron and 

 one of copper, which would have exactly the same geometrical 

 form. After many trials I arranged my trial circuit as follows : 



