1875.] of Bar -magnet s and Conducting -wires. 125 



and below upon the longitudinal magnetism of the movable iron axis 

 and its coil. 



8. As an electric solenoid, however, possesses in some degree many of 

 the properties of a magnet, its longitudinal magnetism, though feeble, 

 must have operated in some of the previous experiments ; and I therefore 

 now tried to obtain rotation of one by the action of vertical currents. 

 Upon a very thin wooden tube 15 centims. long and 12 millims. external 

 diameter I coiled a single stout cotton-covered copper wire from one end 

 to the other, reversing the direction of winding at the middle of the tube, 

 and surmounting the upper end of the wire by a small brass cup con- 

 taining mercury. The lower end of the wire was sharply pointed, and 

 the coil was supported as in the previous experiment. By passing the 

 current from 6 one-pint Grove's elements arranged as 3, faint signs of 

 rotation were observed. 



9. In each of these cases of rotation an upward vertical current 

 entering a lower south pole or leaving an upper one caused the upper 

 end of the rod to rotate in the direction of the hands of a watch, and a 

 downward current entering or leaving a north pole also produced that 

 direction of motion, and reversing the poles in either case reversed the 

 effect. 



10. In each of these instances of rotation, without the aid of a current 

 near the middle of the magnet, the coil being so constructed that the 

 current in it could not be reversed without reversing that in the fixed 

 conductors near it, reversing the direction of the current did not reverse 

 that of the rotation, because the two acting influences were reversed 

 together ; and therefore each apparatus had its own direction of rotation, 

 either right-handed or left-handed (£*\)*, according to the direction in 

 which its coils were wound. It follows from this that a current the 

 direction of which is alternately reversed will drive the apparatus quite 

 as well as one in one uniform direction. 



11. As the rotation was apparently due to the influence of the tangential 

 poleless magnetism of the portions of vertical current in the fixed con- 

 ductors upon the longitudinal magnetism of the vertical iron axis and its 

 coils, I now endeavoured to increase the effect. For this purpose I sub- 

 stituted for the upper brass rod a fixed coil consisting of one layer of 

 copper wire upon an iron wire axis, but having dissimilar poles at its 

 ends and no poles at its middle part, and placed between it and the 

 lower brass rod a similar right-handed one to that described in paragraph 

 6 and free to rotate. The opposed poles of the fixed and movable 

 coils were of opposite kinds, i. e. north and south. On passing a 

 current from a Noe's thermopile of 96 elements f connected as 24, rapid 

 rotation in a right-handed direction occurred. I now substituted for the 



* By a " right-handed " coil, I mean one the upper end of which rotates in the 

 same direction as the hands of a watch. 



t I haye found this apparatus very convenient for such experiments. 



