ON TRANSIENT ELECTRIC CURRENTS. 365 



The observations recorded by Matteucci are very few in number. 

 He gives only four galvanometer readings for each experiment. In 

 spite of the scantiness of his data, we can see in a general way whal 

 form his transient current curves will have. In all cases, the tran- 

 sient current increases at first with the number of cells used, but 

 always decreases when 10 cells are used. This shows that the tran- 

 sient carrent curve will have a maximum point, and must be similar 

 in form to these obtained in the experiments described above. From 

 this we may also estimate roughly the strengths of the magnetizing 

 field used by Matteucci. These facts indicate that the direction of 

 the current as stated by Matteucci, if not an accidental mistake, must 

 be due to some other cause than that suggested by Professor Ewing. 



The transient current developed in twisted steel wires was 

 examined by the method of reversal, as was done for iron. The wire 

 was twisted through ±60°. and the strength of the magnetizing force 

 gradually increased. The direction of the magnetizing current was 

 reversed, and the reading of the galvanometer magnet was noted. 

 Two specimens of steel wires were examined. The one had a 

 diameter of 1.28 mm., and the other 1.50 mm. Plotting the read- 

 ings on the galvanometer scale, Fig. VII. was obtained. The current 

 increases as the magnetizing force is increased. Ultimately it reaches 

 a maximum, and then gradually begins to diminish. The transient 

 current flows in the same directum as in iron. The only differences, 

 which will be apparent at a glance, are the comparative small ness of the 

 current and the higher magnetizing force corresponding to the max- 

 imum transient current. For wires of nearly the same thickness, the 

 transient current in steel does not amount to more than a fourth part 

 of that in iron. On the other hand, the maximum current in steel 

 occurs in a stronger magnetizing field than in iron, as the comparison 

 of the curves represented in Figs. V. and VII. will show. 



