ELE 



ELE 



evolved at the nenrative pole from 

 sulphuric acid, is the result of the ev- 

 olution of hydrogen at that pole. In 

 all cases of true electrolytic action, 

 sulphur appears at the anode. 



ELECTRO-MAGNETISM. "When 

 a current of electricity is traversing 

 any substance, or when electricity is 

 in motion, magnetism is at the same 

 time developed. This fact was first 

 observed by Professor Oersted of Co- 

 penhagen, and has become the source 

 of an important series of discoveries 

 included under the above term. The 

 excitation of magnetism depends 

 upon quantity of electricity, and is 

 best observed in the \\ ire which clo- 

 ses the voltaic circle, especially of 

 one or more pairs of large plates. If 

 a magnetic needle be brought near a 

 wire through which an electric cur- 

 rent is passing, it will immediately 

 deviate from its usual position, and 

 assume a new one, dependant upon 

 the relative position of the needle and 

 the wire. On placing the electric 

 wire above and parallel to the mag- 

 net, the pole next the negative end 

 of the battery always moves to the 

 west ; and when the wire is placed 

 under the needle, the same pole turns ! 

 to the east. "S^'hen the electric wire ; 

 is on the same horizontal plane with 

 the needle, no declination takes place ; 

 but the magnet shows a disposition \ 

 to move in a vertical direction, the 

 pole next the negative side of the 

 battery being depressed when the wire 

 is to the west of it, and elevated when 

 it is to the east. I 



The magnetic phenomena of a wire ! 

 transmitting electricity are such as 

 appear to depend upon the circula- 

 tion of magnetism at right angles to 

 „ the electric cur- | 



>_l p rent, so that if N 

 P represent the 

 wire transmitting a current of elec- 

 tricity in the direction of the hori- 

 zontal darts, a current of magnetism 

 will be established in the direction 

 of the vertical dart, appearing to 

 move round the axis of the electric 

 current ; hence the term vertiginous 

 or rotary magnetism, applied to these 

 phenomena ; and hence the motion j 



IS 



of the pole of the magnet round tho 

 electric wire, or of the electric wire 

 round the pole of the magnet, when 

 they respectively are so arranged as 

 to be able to move freely in any di- 

 rection. If a steel needle be placed 

 in contact with the electric wire, and 

 parallel to it, it acquires opposite 

 magnetisms upon its two sides ; but 

 if it be placed at right angles to the 

 connecting wire, it becomes polar, 

 and permanently magnetic, 

 electric wire be 

 twisted into a 

 spiral, and the 

 steel needle pla- '*' 

 ced within it (as in the cut), it 

 retained there, and becomes a more 

 powerful magnet in consequence of 

 the repetitions and direction of the 

 electric and magnetic currents, as 

 will be evident from the annexed fig- 

 ure, where a represents a glass tube 

 with the wire n p conveying the elec- 

 tric current twisted round it, the darts 

 at the ends of which show the ingress 

 and egress of the electricity, and the 

 transverse darts the direction of the 

 magnetic current. If the cylinder 

 round which the wire conveying the 

 electric current is twisted be of steel, 

 it becomes a permanent magnet ; if of 

 pure soft iron, it becomes a temporary 

 magnet, so long as the electric current 

 is in motion, and s and 7i are 

 powerfully opposed poles. If 

 the bar be bent, as in the an- 

 nexed cut, a powerful horse- 

 shoe magnet is obtained 

 when the ends, p n, of the 

 copper wire twisted round 

 it are connected with the voltaic cir- 

 cle ; and a single pair of plates is suf- 

 ficient for the purpose. 



ELECTROMETER (from n^.ea- 

 Tpov, and fxerpov, a measure). An in- 

 strument for ascertaining the pres- 



A 



=T 



ence and intensify of electric excita- 

 tion. The simplest form of electrom- 



255 



