Nipher — Local Magnetic Storms. 61 



All of this evidence indicates conclusively, that the 

 apparent increase in the strength of the deflecting mag- 

 net when in contact with the terminal of the machine, is 

 due to an increase in the permeability of the air around 

 the magnet. 



The '' charged" molecules of air appear to behave 

 like iron filings, in that they set in the field of the deflect- 

 ing magnet with the planes of the electrical whirls at 

 right angles to the lines of force. It was found that a 

 solid steel magnet gives similar results.* 



The electrified magnet was placed in a glass tube hav- 

 ing an internal diameter of about 4 cm. The tube ex- 

 tended to the metal shield enclosing the needle. This 

 metal shield was grounded. It was then found that the 

 deflecting effect of the magnet was less, than when the 

 magnet was not connected with the influence machine. 

 When the machine is stopped, the deflection at once be- 

 comes greater than normal, but it quickly diminishes 

 to normal value. The reason for this was explained, 

 by filling the tube with tobacco smoke before the machine 

 was started. The column of air within the tube was in 

 continual commotion while the machine was in oper- 

 ation. The molecules of ionized air could not then set 

 in orderly array along the lines of force. It is remark- 

 able that under such conditions, the permeability of the 

 air-column is less, than when the magnet is not in com- 

 munication with the machine. 



When the insulated magnet was enclosed in a mass 

 of cotton batting, having a diameter of about 50 cm., 



*A bar magnet thus used as a deflecting magnet, over whicli a 

 sheet of glass is placed, extending to the shield around the needle, 

 gives most interesting results when the plate is sprinkled with iron 

 filings. The increase in permeability due to tapping the plate is 

 plainly evident. When the filings are gathered in a heap at the 

 equator of the magnet, its deflecting effect is greatly diminished. If 

 at any point in the field of this magnet, the iron filings are disturbed 

 by means of a brush, the magnetic field will be disturbed throughout. 

 If the iron filings were free to move, they would respond to the dis- 

 turbance. The suspended needle does respond. 



