AB be a conductor in which a current is flowing in the direc- 

 tion of the arrows, and rising in value. Lines of force E rise 

 out around AB and cut the neighboring conductor CD, setting 

 up a pressure in it, opposite in direction to the current flowing 

 in AB. If CD be a closed circuit, a current will How in CD in 

 the direction of the arrows. The lines of force E as they cut 

 CD, tear the electrons out of the atoms of the copper and set 

 them to flowing in the direction indicated. When the current 

 in AB becomes steady, the current in CD ceases to flow. It is 

 necessary that the lines of force be moving and cutting at an 

 angle across the circuit CD in order to set up a current in it. 



When these lines of force fall in upon AB, they set up a 

 current in CD flowing in the same direction as the current in 

 AB. On account of the above phenomena it is necessary to as- 

 sume that the lines of force have direction. 



Figure 1. 



The nature of the field that exists around a moving neg- 

 ative charge can thus be studied, since the electric current con- 

 sists of a stream of negative charges. The field about a moving 

 positive charge cannot be studied, because the positive charge 

 does not flow in a conductor, and when it does How as in an 

 electrolyte, it is always associated with a negative charge, the 

 two flowing in opposite directions. In this case also their move- 

 ment is very slow, since both charges are associated with atoms. 

 In the voltaic cell and the electrolytic cell, the flow of electrons 

 that constitutes the electric current is also associated with the 

 movement of these charged atoms, or ions. 



When the cathode ray or ultra violet light falls upon a 

 gas, the gas becomes ionized. In order to account for this J. 

 J. Thomson assumed that the radiations knock electrons or 

 negative charges out of the neutral atoms. An atom minus 

 an elestron then becomes positively charged. The separated 

 electrons associate themselves with neutral atoms. An atom 

 plus the electron is negatively charged. 



Thomson thus supposes that the atoms of all elements are 

 made up of electrons on the one hand and a positive portion 

 or matrix, with which the electrons associate themselves. This 



58 



