Account of Experiments with a powerful Electro-magnet. 33 



removed to a considerable distance from the surface of the iron, 

 I proceeded to fit up the large bar already described with a coil 

 consisting of a bundle of copper wires 68 yards long, and weigh- 

 ing 100 lbs. The electro-magnet thus formed was placed in a 

 wooden box, on the side of which two large brass clamps were 

 screwed, the latter being soldered to the terminals of the coil. 

 The accompanying sketch represents the apparatus in its com- 



pleted state ; excepting, however, two brass straps, by means of 

 which the coil is kept securely in its place, which are omitted for 

 the sake of clearness. 



In experimenting with the electro-magnet, I employed a bat- 

 tery consisting of sixteen Daniell's cells, the copper of each 

 exposing an active surface of nearly two square feet. They were 

 arranged so that I could with facility use either one cell alone, 

 four cells in a series of two, or sixteen in a series of four elements. 

 The cells and the liquids in them being similar in every respect, 

 it was evident that these arrangements must produce through 

 the electro-magnetic coils currents represented by 1, 2 and 4. 

 I therefore was enabled to dispense with the use of a galvano- 

 meter, which would have been acted upon by the powerful elec- 

 tro-magnet, even if it had been placed at the distance of many 

 yards from it. 



Experiment I. — A magnetic needle, 1~ inch long, was sus- 

 pended at the distance of three feet from the electro-magnet 

 measured on a line at right angles to that joining the poles. 

 The northward tendency of the needle having been counteracted 

 by means of a permanent magnet, I observed the following 

 vibrations per minute resulting from the action of the electro- 

 magnet : — 



With 1 cell in a series of 1 . . 48 vibrations. 



... 4 cells ... 2 . . 63 



... 16 ... 4 . . 96 



The vibrations are evidently in the ratio of the square root of the 

 quantity of current circulating around the electro-magnet, and 

 consequently we may infer that the magnetism induced in the 

 latter was simply in proportion to the current. 



Phil. May. S. 4. Vol. 3. No. 15. Jan. 1852. D 



