330 Electro-Magnetic Experiments. 



Tlie weight of the horse-shoe, together with its surrounding spiral 

 wire, was about five pounds.* A piece of soft iron, constructed in 

 the same form as the iron which connects the ends or poles of a 

 horse-shoe, or armed magnet, weighed about one and a quarter 

 pound or six hundred and thirty grammes. 



The galvanic apparatus used consisted of one single copper trough, 

 in which a zinc plate was immersed. The acting surface of this zinc 

 plate was about eleven English square feet. 



When the conducting fluid was poured into the trough, the horse- 

 shoe immediately became a strong magnet, capable of supporting 

 about twenty-five kilogrammes or fifty pounds. 



If vi^eights are added with some caution, this extempore magnet 

 may be brought to support seventy-five pounds or thirty-eight kilo- 

 grammes. 



The south pole of the horse-shoe magnet is on that side on which 

 the copper spiral wire is dipped in the cup connected with the zinc 

 plate ; the north pole, of course, is on the side communicating with 

 the copper trough. 



We call tlie north pole of a magnet that end of it which, in a mag- 

 netic needle, points to the north. 



The rapidity with which such a powerful magnet, capable of sup- 

 porting seventy-five pounds, is produced, is truly astonishing. With 

 equal celerity the magnetism is destroyed and the poles reversed, 

 merely by shifting the connecting wires of the battery from one cup 

 to another. 



The magnetism of this horse-shoe is not, however, instantaneously 

 destroyed, merely by taking the connecting wires out of the cups, and 

 without shifting them from one cup to another. Instead of suspend- 

 ing from the magnet the maximum of what it is able of supporting, if 

 a lesser weight, twenty pounds or ten kilogrammes be attached to it, 

 the magnet will not cease to support the weight, immediately after 

 removing the wires from the cups, but continue to attract the weight 

 for a longer or shorter time, according to the strength of the magnet. 

 The heavier the weight which remains thus suspended, the shorter 

 will be the time after which it falls down. 



* Tlic pounds mentioned here, are Dutch weiglit, oi' sixteen ounces in the pound. 

 This is somewhat lieavler than avoirdupois. Two pounds arc a little less than one 

 kilogramme. But if no great accuracy is required, two pounds may be estimated 

 equal to one kilogramme. 



