654 HENRY A. EOWLAND 



which has the water at rest. Again, I have here two wires, alike in all 

 respects, except that one has a current of electricity flowing in it and 

 the other has not. But in this case I have only to bring a magnetic 

 needle near the two to find out in which one the current is flowing. On 

 our ordinary sense the passage of the current has little effect; the air 

 around it does not turn green or the wire change in appearance. But 

 we have only to change our medium from air to one containing magnetic 

 particles to perceive the commotion which the presence of a current 

 may cause. Thus this other wire passes through the air near a large 

 number of small suspended magnets, and, as I pass the current through 

 it, every magnet is affected and tends to turn at right angles to the wire 

 and even to move toward it and wrap itself around it. If we suppose 

 the number of these magnets to become very great and their size small, 

 or if we imagine a medium, every atom of which is a magnet, we see that 

 no wire carrying a current of electricity can pass through it without 

 creating the greatest commotion. Possibly this is a feeble picture of 

 what takes place in a mass of iron near an electric current. 



Again, coil the wire around a piece of glass, or indeed, almost any 

 transparent substance, and pass a strong current through the wire. 

 With our naked eye alone we can see no effect whatever, as the glass is 

 apparently unaltered by the presence of the current; but, examined in 

 the proper way, by means of polarized light, we see that the structure of 

 the glass has been altered throughout in a manner which can only be 

 explained by the rotation of something within the glass many millions 

 of times every second. 



Once more, bring a wire in which no current exists nearer and nearer 

 to the one carrying the current, and we shall find that its motion in such 

 a neighborhood causes or tends to cause an electric current in it. Or, if 

 we move a large solid mass of metal in the neighborhood of such a cur- 

 rent we find a peculiar resistance unfelt before, and if we force it into 

 motion, we shall perceive that it becomes warmer and warmer as if there 

 was great friction in moving the metal through space. 



Thus, by these tests, we find that the region around an electric cur- 

 rent has very peculiar properties which it did not have before, and 

 which, although stronger in the neighborhood of the current, still ex- 

 tend to indefinite distances in all directions, becoming weaker as the 

 distances increase. 



How great, then, the difference between a current of water and a cur- 

 rent of electricity. The action of the former is confined to the interior 

 of the tube, while that of the latter extends to great distances on all 



