108 Nichols and Franklin — Direction of Electric Currant. 



had been found that its indications when heated by an alterna- 

 ting current of the character used in our experiments agreed 

 very closely indeed with those obtained by calibration with con- 

 tinuous currents of known intensity. Such a calibration was 

 made in the present case, covering deflections from zero to 300 

 scale-divisions, which last-named reading corresponded to 5 # 00 

 amperes. 



The new coil of 390 turns was now driven at 380 revolutions 

 per second, the circuit being opened and closed and the cur- 

 rent direction through the coil being repeatedly reversed, as in 

 the former experiments. The amount of current traversing 

 the coil was increased from time to time until the stretched 

 wire indicated 4 - 26 amperes of alternating current, which was 

 the largest quantity which it was deemed safe to permit the 

 coils to carry, even for the few seconds necessary to the com- 

 pletion of an observation. The direction in which the coil re- 

 volved was likewise reversed from time to time. No change 

 in the position of the needle due to the motion of the coil, nor 

 to a reversal of the direction of the coil, nor to a reversal of 

 the direction of the current within the coil could be detected, 

 although" the sensitiveness of the needle had been increased, 

 about eight times, the current more than four times and the 

 number of turns in the ratio of 390 to 64. 



A re-determination of the figure of merit of the apparatus 

 showed that l mm deflection now corresponded to '00000043 am- 

 peres. An effect of much less than l mm due to the revolution 

 of the coil, would have been clearly observable under the con- 

 ditions of the experiment. The absence of such an effect 

 seemed to warrant us in the conclusion, that if direction be as- 

 cribed to the electric current, its velocity must be such that the 

 quantity of electricity conveyed past a given point in a unit 

 of time, when the direction of the current was that in which 

 the coil was travelling, did not differ from that transferred 

 when the current and coil were moving in opposite directions 

 by as much as one part in ten million — even when the linear 

 velocity of the wire, as in our experiment was 90968 centi- 

 meters. 



Now the velocity at which such a current must needs have 

 traveled, in order that the revolution of the coil should in- 

 crease or diminish the quantity of electricity passing the needle 

 by an amount corresponding to a deflection of l mm , or in the 

 case of the reversal of the direction of the current within the 

 moving coil, corresponding to 2 mm , is found as before by multi- 

 plying the current in the coil by the linear velocity of the 

 latter and dividing the product by the figure of merit of the 

 apparatus. 



