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Akt. VIII. Description of an Electro-magnet ical Jpparatu s 

 for the Exhibition of Rotatory Motion. Bi/M. Faraday, 

 Chem. Assist, in the Royal Institution. 



The account given in the Miscellanea of the last Journal, of 

 the apparatus invented in illustration of the paper in the body 

 of that Number, being short and imperfect ; a plate is given in 

 the present Number, presenting a section of that apparatus, 

 and a view of a smaller apparatus, illustrative of the motions 

 of the wire and the pole round each other. The larger appara- 

 tus is delineated, Fig. 1. Plate VII. on a scale of one-half. It 

 consists of two glass vessels, placed side by side with their ap- 

 pendages. In that on the left of the plate the motion of a mag- 

 netic pole round the connecting wire of the voltaic battery is 

 produced. That a current of voltaic electricity may be esta- 

 blished through this cup, a hole is drilled at the bottom, and into 

 this a copper pin is ground tight, which projects upwards a 

 little way into the cup, and below is rivetted to a small round 

 plate of copper, forming part of the foot of the vessel. A simi- 

 lar plate of copper is fixed to the turned wooden base on which 

 the cup is intended to stand, and a piece of strong copper wire, 

 which is attached to it beneath, after proceeding down- 

 wards a little way, turns horizontally to the left hand, and 

 forms one of the connexions. The surfaces of these two 

 plates mtended to come together, are tinned and amalgamated, 

 that they may remain longer clean and bright, and afford 

 better contact. A small cylindrical and powerful magnet has 

 one of its poles fastened to a piece of thread, which, at the 

 other end, is attached to the copper pin at the bottom of the 

 cup ; and the height of the magnet and length of the thread is 

 so adjusted, that when the cup is nearly filled with clean mer- 

 cury, the free pole shall float almost upright on its surface. 



A small brass pillar rises from the stand behind the glass- 

 vessels : an arm comes forward from the top of it, supporting 

 at its extremity a cross wire, which at the place on the left 

 hand, wliere it is perpendicularly over the cup just described, 

 U 2 



