126 ■ Mr. G. Gore on the Rotations [Dec. 9, 



lower brass rod another fixed coil, similar to the upper one, but of an 

 opposite direction of polarity, and passed the current again ; still more 

 rapid rotation in the same direction took place, and the effect was very 

 striking. In this latter instance two south poles free to move were 

 opposed to two fixed north poles, and in each instance the current was 

 passed upwards. In the second experiment also the longitudinal 

 magnetic influence of each opposed iron axis and coil acted upon the 

 tangential magnetism of the longitudinal element of the end of the 

 copper coil-current opposed to it, and thus both the longitudinal and the 

 tangential magnetism of each of the four opposed ends cooperated to 

 produce a most effective result. 



With a thicker axial wire in the moving coil the rotation was not so 

 rapid ; and with an axial wire of the usual thickness, but a double layer 

 of copper-wire coils, and the current passing through the axial wire, the 

 rapidity of rotation was not much altered, probably because the increased 

 weight and friction counteracted the effect of the increased magnetism. 

 By substituting for the right-handed movable coil with south poles at 

 its extremities, in these experiments, a left-handed one with north poles 

 at its ends opposed to north poles of the fixed ones, and passing the 

 current, no rotation occurred : in this case the longitudinal element of 

 the current in the movable coil, acting upon the longitudinal magnetism 

 of the fixed iron axis and its coil, tended to produce rotation in one 

 direction, and the longitudinal magnetism of the movable axis and its 

 coil, acting upon the longitudinal element of the current in the fixed coil, 

 tended to produce rotation in the opposite direction. 



12. I now substituted for the movable coil a vertical wire of iron 

 13 centims. long and 1*7 millim. diameter, surmounted by a small 

 brass mercury-cup, passed the current from the thermopile, and ob- 

 tained rotation, but less rapid than before, probably because of the 

 less degree of longitudinal magnetism ; but by enclosing this wire in the 

 axis of a fixed coil which produced appropriate and similar poles at its 

 two ends, as in paragraph 4, and repeating the experiment, very great 

 velocity of rotation was obtained. Rotation of a somewhat thicker wire 

 of nickel was also obtained, both with and without the aid of the current 

 in the middle fixed coil. I also tried, without the aid of the middle fixed 

 coil and with it, a copper wire of similar dimensions to the iron one, 

 and obtained rotation freely : in this case the motion was probably nearly 

 wholly due to the action of the longitudinal magnetism of the adjacent 

 ends of the fixed axial wires and their coils upon the tangential magnetism 

 produced in the movable copper wire by the axial current. Each of these 

 rotations agreed in direction with those of the movable coil. 



13. The apparatus represented in fig. 2 was employed for nearly 

 all the various modifications of the experiment, by substituting for one 

 or more of the coils metallic wires &c. as desired. The upper part 

 of the brass pillar A was capable of sliding in the lower part B, and 



