ELECTKO-MAGNETISM. 437* 



drop more is forced into the tube at "Washington, a drop must fall out at 

 New York, but no drop is caused to pass from Washington to New York, 

 Something Uke this occurs in the transmission of electricity. 



812. Electricity, through an electro-macr^ 



Can electricity . •' ' » -i i i ,^ 



be miide to nctic arranoeiuent, can be made available lor 



measure time t " „ . . , . 



the measurement ot time, and by its agency a 

 great number of clocks can be kept in a state of uniform 

 correctness. 



The plan by which this is accomplished is substantially as follows : — A bat« 

 tery being connected with a principal clock, which is itself connected by 

 means of wires with any number of clocks arranged at a distance from each 

 other, has the current regularly and continually broken by the beating of the 

 pendulum. This interruption is also experienced by all the clocks included 

 in the circuit; and in accordance with this breaking atid making of contact, 

 the indicators or hands of the clock move over the dial at a constantly uniform 



rate. 



813. The fundamental law of action in frictional electricity 

 action o'f elec- ^^' *'^^* ^o^ies charged with like electricities at rest repel, and 

 tricai currents with unlike, attract each other. With electricity in motion 

 other? * ^^^ ^^^^ ^ somewhat different, since currents of the same 

 electricity moving in the same direction attract each other. 

 The general law of this action may be stated as follows : 



,,^ , . ,^ If electric currents flow in Avires parallel to 



What IS the 1 



generaiiaw of each othep, aud have freedom of motion, the 



this action ? , . ' , 



Wires are immediately disturbed. If the cur- 

 rents are moving in the same direction, the wires attract 

 each other ; if they are moving in opposite directions, 

 they repel eadh other : or, like currents attract, and un- 

 like repel. 



How may a he- ^14. Whcn the wircs connecting the positive 

 ed inloTraagI ^^d ucgativc polcs of a galvanic battery in ac- 

 netic needle? ^[^^ ^rc coilcd in the form of a helix, the helix 

 becomes possessed of magnetic properties. If such a 

 helix be suspended in a horizontal plane, it points, as a 

 magnetic needle would, north and south ; if ifc is sus- 

 pended so as to move in a vertical plane, it acts as a dip- 

 ping needle. 



If two helices carrying currents are presented to each other, they attract 

 and repel, precisely as if they were magnets, according as like or unlike poles 

 are brought together. And, in short, all the properties of the magnetic neecil* 

 may bo imitated by a helix carrying a current. 



