148 HOUSTON, KENNELLY — THE PATH OF A CURRENT. [Mar. 19, 



meate the air and ether in the room, but there will be no magnetic 

 flux present, except that due to the earth's magnetism. As soon, 

 however, as any motion occurs in an electric flux, either by moving 

 the charge on the body, or by causing it to increase or decrease 

 in density, the disturbance in electric flux temporarily produces a 

 magnetic flux; and, generally speaking, any variation or motion of 

 electric flux produces magnetic flux. 



A permanent magnet produces magnetic flux, both in its sub- 

 stance and in the space surrounding it. So long as the distribu- 

 tion of magnetic flux remains quiescent, no electric flux is pro- 

 duced. As soon, however, as any change takes place in the mag- 

 netic flux, either, by bodily moving the magnet, or by weakening 

 or strengthening the magnet, electric flux is temporarily produced.. 

 Generally, any variation or motion of magnetic flux produces elec- 

 tric flux. 



Magnetic flux is always circuital, or is distributed in stream lines 

 which form closed curves, or have reentrant paths. Electric flux, 

 when established between opposite electric charges, is not circuital, 

 but terminates at one end in one charge, and at the other end in the 

 opposite charge. When, however, electric flux is established by 

 magnetic disturbances in a space free from conductors, it is circuital, 

 like magnetic flux. 



Both electric and magnetic flux possess both direction and 

 polarity ; that is to say, each is developed along definite stream lines, 

 and each possesses different properties up and down such stream lines. 

 An analogy is presented mechanically in a stream of water. Water 

 in a river flows in stream lines, and is directed in its motion down 

 stream. In the case of electric flux the polarity is manifested by 

 what are called positive and negative charges, these charges being 

 developed where the electric flux terminates. In the case of mag- 

 netic flux the polarity is manifested by what is called north-seeking 

 poles and south-seeking poles. These poles are developed where 

 the magnetic flux terminates on the magnet. For this reason electric 

 flux is conventionally assumed to leave a positive charge and, to 

 terminate, on arrival at a conductor, at a corresponding negative 

 charge. This, while being a purely arbitrary assumption, is, never- 

 theless, advantageous in fixing ideas. Similarly, magnetic flux is 

 assumed to issue from a magnet at its north-seeking pole and to 

 reenter it at its south-seeking pole. This assumption is also purely 

 arbitrary. 



