shows that the speed of the electrons through conductors is 

 very great. ' 



Rutherford measured the mass and charge of the alpha 

 particle emitted by radium, and found it to be about the mass 

 of the hydrogen atom, and to have ;i charge equal in value to 

 the charge on the electron. These positively charged alpha 

 particles have been found to be positively charged helium 

 atoms. 



Goldstein demonstrated the existence of positive charges 

 in a Crooke's tube. A small hole was pierced in the cathode 

 and positive charges appeared behind the cathode. They were 

 called "canalstrahlen." When measured, the mass of these 

 particles was found to be about the mass of the hydrogen atom 

 and the charge was found to be opposite to but equal in value 

 to the charge of the electron. 



Wellisch in the Cavendish laboratory, Cambridge, has 

 lately measured the mass and charge on the particles which 

 constitute the canalstrahlen, when produced in tubes contain- 

 ing different gases. He found this mass and charge to be the 

 same no matter what gas the tube might contain. 



Since the atomic weights of the various gases is very dif- 

 ferent from that of hydrogen or helium, this seems to indicate 

 the existence of a positive entity, having the mass of helium 

 or hydrogen. Whether the actual positive entity is merely 

 contained upon or included in this positive particle, or whether 

 it is a small mass the size of the electron hut opposite in charge 

 is not yet known. The fact is however that the smallest posi- 

 tive charge known is atomic in size, consequently it cannot tlow 

 through a metallic conductor. 



Thus the electron theory of electricity assumes that the 

 electric current consists of a stream of negative charges or 

 electrons. This theory also assumes that the electrons flow 

 from the positive to the negative pole of the battery on the 

 outside of the cell. 



A current of electricity or a stream of negative charges 

 sets up an electromagnetic Held around the conductor in which 

 it is flowing. The lines of force which constitute this field are 

 assumed to be rotating right-handedly around the wire with 

 their plane of rotation perpendicular to the axis of the wire. 



According to the right-hand rule: "If the conductor be 

 grasped in the right hand, the thumb pointing in the direction 

 in which the current is flowing, the fingers encircle the con- 

 ductor in the direction in which the lines of force are supposed 

 to be rotating." 



When a current of electricity or a stream of electrons 

 starts to tlow in a conductor near a neighboring conductor, a 

 current of electricity is found to he flowing in the opposite di- 

 rection to the current in the first named conductor. This cur- 

 rent is called an induced current, and the process is known as 

 induction. This process takes place as follows: In Fig. 1 let 



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