244 Mr. Sturgeon on Electro-Magnetism. 



ring that time by gentlemen eminent in this branch of philo- 

 sophy, and who have uniformly acknowledged it to be an 

 imposing and pleasing spectacle. It is now ottered, with some 

 others which it is presumed are the first of the kind, and which 

 possibly may not be thought uninteresting to some of your 

 readers. 



Description of the Apparatus. 



Fig. 1 (PI. II.) mN??, sSs, a brass cylindrical tube contain- 

 ing seven bar magnets, each of which is eight inches long. 

 These magnets are placed in a frame in the lower part of the 

 cylinder, the upper end of which being moveable can be taken 

 off at any time to change their position for the purpose of 

 varying the experiment. Fig. 2 is a transverse section of the 

 cylinder with its magnets. 



As the like poles of the magnets are all placed in the same 

 end of the tube when used, the latter with its contents may 

 be considered as a compound cylindrical magnet. At the 

 lower end S of the cylinder is a stout brass stud T, which 

 stands firm in a socket on the top of the foot A. Around this 

 socket is a cell for the purpose of holding quicksilver. An- 

 other cell ece fits gently on the outside of the cylinder, and is 

 suspended over its top part by a stout brass wire w w, the ex- 

 tremities of which communicate with the mercury in the cell 

 cce; another connecting wire ff communicates with the 

 mercury in both cells. Cc Cc is a copper vessel made in 

 the form of an Ampere's rotating cylinder, seven inches in 

 diameter ; in this vessel is placed a cylinder of zinc, as repre- 

 sented by the dotted lines zz. On the outer rim, and at 90° 

 from each other, are soldered four brass studs ; to the ex- 

 tremities of which are soldered two brass wire circles (one 

 only of which is shown in the figure) that cross each other at 

 right angles in the pole P; from which junction descends a 

 pivot that runs in a hole made to receive it in the upper part 

 of the connecting wire "ww. The two circles are each 9| inches 

 diameter, and form two great circles of the sphere they are 

 intended to represent. The lower parts of the circles are left 

 open and the points of the wires bent downwards till they 

 come in contact with the mercury in the lower cell. Two 

 other wires proceed from the upper edge of the zinc cylinder, 

 and terminate in the mercury in the upper cell ece, as shown 

 in the figure. 



Things being thus arranged, when dilute acid is poured 

 into the copper vessel, the galvanic action takes place through- 

 out every part of the great circles which represent the sphere; 

 ascending from the copper in the upper hemisphere HH from 



the 



