104 Nichols and Franklin — Direction and 



flection of the needle might have been looked for as the re- 

 sult of the revolution of the coil ; the deflection being greater 

 when the coil was revolving in " the direction in which the 

 current was flowing than when at rest, and less when the 

 direction of the current was opposed to that of the coil. The 

 result of the experiment was a negative one, the deflection of 

 the needle being just the same when the coil was at rest as 

 when it was in rapid rotation. 



Fceppl's apparatus was inadequate to the end in view, for 

 had the current consisted in a motion of translation of a sin- 

 gle fluid, its velocity need not have greatly exceeded 300,000 

 centimeters per second to have rendered the difference between 

 the deflections due to the stationary and to the rotating coil 

 indistinguishable. The method is, however, capable of very 

 much greater refinement than that attained in his experiment, 

 and while modern views of the nature of the electric current 

 are such as to lead us to look for a negative result, whatever the 

 delicacy of the apparatus, the present condition of electrical 

 theory is not such as to render a repetition of the experiment 

 under improved conditions devoid of interest. 



The present writers, by whom the details of a similar method 

 had been developed before they became acquainted with 

 Foeppl's work, have repeated his experiment with an appara- 

 tus capable of indicating the direction and velocity of the 

 current, supposing it to have direction, even though that ve- 

 locity were very large indeed. 



A flat bobbin of hard rubber was carefully turned upon a 

 lathe. It was 8"25 cm in diameter and l*6 cm in thickness. The 

 periphery was provided with a groove of rectangular cross-sec- 

 tion. This groove was wound differentially with sixty-four 

 turns of insulated copper wire. The winding was very com- 

 pact and the wire was held in place within the groove by means 

 of a brass tire or collar. Brass discs of slightly smaller diame- 

 ter than the bobbin were screwed to the faces of the latter and 

 well centered steel axles were inserted in these discs. Two 

 brass supports, fastened to a hard rubber block which served as 

 a base for the apparatus, carried bearings of Babbitt metal in 

 which the steel axles of the bobbin rested. Each of the sup- 

 ports likewise bore two brushes of spring brass which could be 

 so adjusted as to make contact with brass collars upon the axle 

 of the coil. When the supports were connected with the ter- 

 minals of a storage battery or other source of current, the cir- 

 cuit was completed through the coil ; the current passing from 

 one support to the axle upon that side by means of the bearing 

 and brushes, thence to the brass disc upon the same side of the 

 bobbin. From this disc, with which one terminal of the coil 



