360 Mr. Sturgeon's Account of [Nov, 



magnet ; the equatorial trough e is made moveable on the pil- 

 lars g gy and is tixed by the screws h li. 



Fig. 2. A view of a circular metal disk, made to revolve 

 Vetween the poles of a horse-shoe magnet ; the disc is amalga- 

 mated round its edge, and dips into a httle mercury contained 

 in a hollow J of the stand, the centers k k on which it turns, and 

 the hollows that receive them in the forked support II are 

 amalgamated ; the screw m allows the disc to be adjusted, and 

 fixed so as only just to touch the surface of the mercury. A 

 horse-shoe magnet n or n s shown by dotted lines, is laid on 

 the stand, then one of the troughs a of fig. 1 is to be adjusted 

 on its stand b, till its bottom wire z dips into the connecting cup 

 z, forming the zinc communication, and a connecting wire d 

 with bent ends is to dip into the copper connecting cup c of the 

 trough, and into the cup c of the disc ; the communication of 

 the poles being thus made (the current passes from z, through 

 the mercury J, into the edge of the disc, and through its centers 

 k k into the fork / /, and up to the cup c) the disc will then 

 revolve as shown by the arrow. By reversing either the poles 

 of the magnet, or the electric poles, the revolution of the wheel 

 is reversed ; but if both are reversed, the revolution will continue 

 in the same way as at first. The six rays are painted on the 

 disc, merely to render the revolution visible at a greater distance. 



Fig. 3. A stand supporting a needle between two conducting 

 wires o o and pp to show the different effect of electricity on the 

 needle when passing above or below it ; the cup z is common 

 to both, but the other ends have each a separate cup c c : when 

 the electric current passes along the upper wire, pp the needle 

 takes the position as shown in fig. 4 ; but on lifting the connect- 

 ing wire out of the cup p c, and putting it into the cup o c, the 

 current passes through the under wire o o, and the needle imme- 

 diately goes round to the position indicated in fig. 5 ; then if 

 you watch the motion of the needle, and keep alternately trans- 

 ferring the wire out of one cup into the other, keeping time with 

 the needle, you may bring it into the most rapid revolution that 

 you can possibly keep time with. 



Figs. 6 and 7. A front and side view of a stand with two con- 

 necting cups z and c made of wood, in which the bent iron 

 wire wound round with copper wire is supported by the two 

 copper wire ends. On making the galvanic connexion through 

 the copper wire, the iron wire becomes a strong horse-shoe mag- 

 net, and will support a heavy bar of iron as 3/ fig. 7; but on 

 lifting the connecting wire d, fig. 6, out of the cup z, the weight 

 immediately drops, and on restoring the connexion, the power 

 is restored ; then if you change z for c, it will change n for s, 

 or if you only wrap the copper wire about the iron wire, as a 

 right threaded screw instead of a left one, as in the Plate, 

 it will change n for s. This is explained by what takes place 

 in figs 3, 4, and 5. 



