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the power of an electro-magnet ; and the author found that the worst 

 part of a bar of the worst iron he could procure made by far the best. 



A bar electro- magnet, four feet long, which scarcely retained any 

 power when its connexion with the battery was broken, on being re- 

 connected with it, in the same direction as before, was rapidly con- 

 verted into a powerful magnet; but after being removed, and its 

 wires now connected with the opposite poles, it required a long time 

 to convert it into a magnet of much inferior power; as if the atoms 

 of electricity, having been first put in motion in one direction, are 

 afterwards more easily turned in that direction than in the contrary. 



The author failed in his attempts to make a permanent horse-shoe 

 magnet of tempered steel by the touch, with an electro-magnet: not 

 the slightest trace of magnetism was communicated to the steel ; on 

 the contrary, a previously magnetized horse-shoe magnet had its 

 power completely destroyed by similar means. 



Dr. Ritchie describes a method of making an electro-magnet re- 

 volve in a horizontal direction about its centre, by permanent mag- 

 nets properly arranged. This method consists in changing the poles 

 of the soft iron magnet the moment it passes the pole of the steel 

 magnet, so that attraction is almost instantaneously changed into re- 

 pulsion, and the motion rendered continuous. 



In the third part the author describes a mode of obtaining a con- 

 tinuous current of electricity by the induction of common magnets. 

 Any number of soft iron cylinders, having a coil of copper ribbon 

 covered with thin tape wound round the middle, are fixed in such a 

 manner to a revolving table, that they can be brought in rapid suc- 

 cession opposite to the poles of a permanent horse-shoe magnet : the 

 soft iron cylinders are thus converted into temporary magnets. The 

 copper ribbons are so connected, by means of wires soldered to their 

 ends, with well amalgamated discs beneath, that their contact with 

 them is successively made and broken, as often as the soft iron cylin- 

 ders pass opposite the poles of the permanent magnet : and a delicate 

 galvanometer is made to form part of the circuit. On putting the re- 

 volving table into rapid motion, an electric state is induced on the 

 copper ribbon, and consequently on the continuous circuit, from the 

 moment the magnet has begun to act on it till it has acquired its 

 state of greatest magnetic power. The connexion being then broken, 

 by the wire attached to the end of the copper ribbon leaving the amal- 

 gamated disc of copper beneath, the needle would return to its former 

 position were it not prevented by the formation of a new current, from 

 the next cylinder of iron coming within the action of the magnet ; 

 and, by employing a greater number of magnets, the developement of 

 the fresh current may be effected before the preceding one has been 

 broken off, and the needle be thus made to show a steady deflection. 



The author failed in all his attempts to effect chemical decompo- 

 sition, even of the most easily decomposable compounds, by means of 

 the nearly constant current of electricity produced by his present ap- 

 paratus ; and previous to making a more powerful one, he wished to 

 ascertain whether water be a conductor of electricity thus developed, 

 or not. For this purpose a film of hot water, of more than fifty square 

 inches, was made to form part of the circuit of the magneto-electric 



