258 



GENERAL SCIENCE 



CONNECTED CELLS 



The cells in the upper row 

 are connected in parallel; those 

 in the lower row, in series. 



mon dry cell in good condition has an E. M. F. of about 

 two volts. 



A battery consists of a number of cells connected in 

 series or in parallel. When cells are in parallel the positive 



poles are joined to positive 

 poles and the negative poles 

 to negative poles. When cells 

 are in series they have the 

 positive pole of one connected 

 with the negative pole of the 

 next and so on. The E. M. 

 F. increases when cells are con- 

 nected in series, and the cur- 

 rent increases when they are 

 connected in parallel. 

 180. Magnetic Field about a Current. From the 

 chapter on magnets we found that a magnet has a mag- 

 netic field about it and that the lines of force come from 

 the N pole and pass through the air to the S pole, and 

 that a small compass, while held in the magnetic field, 

 points in the direction in which the lines of force are 

 going. To show this, connect two or more electric cells 

 in parallel and have part of the wire of the external cir- 

 cuit in a vertical position and passing through a sheet 

 of paper as shown in the illustration. Sift some very 

 fine iron filings on the paper and jar the paper very 

 gently to cause the filings to adjust themselves to the 

 magnetic lines of force going around the wire. It will be 

 found that the wire is in the center of all the circles 

 formed. Now place one or more small compasses on the 

 paper near the wire and determine which way the lines 

 of force are traveling. The compass needle will point 

 in the direction in which the lines of force go. 



