Scientific Lectures. 151 



another ; and now I have six rings suspended from this stout iron 

 rod, yet none of this mass of suspended iron touches the magnet. 

 The battery wire is now detached and the rings fall to the floor.* 



There is, however, another condition, besides mere proximity to 

 the magnet, which is necessary for magnetization at a distance, and 

 that is the part of the magnet toward which the iron bar points. 

 Only with the great power of this huge magnet can I clearly show 

 you this important truth, and without it a link in the chain of my 

 reasoning toward the solution of our problem would be wanting. I 

 hold in my hands a bar of soft iron four feet long ; I bring this 

 toward the center of the great magnet and point it at right angles to 

 its length. Observe, it is powerless to hold up even a nail. Hold- 

 ing the bar at the same distance, I now point it toward one end of 

 the magnet, and see the difference ; how the spike and rings adhere 

 to it ; for as long as the bar points toward the end of the magnet it is 

 magnetized ; but observe, as I slowly rotate the bar around the end 

 nearest the magnet — spike and ring are falling to the floor, and now 

 that it points again toward the center of the magnet it is powerless. 

 Therefore direction as well as proximity is necessary for the mag- 

 netization of a bar by induction. 



With the knowledge of the method I have given you to distin- 

 guish between a mere magnetic substance which is attracted indif- 

 ferently by either pole of a magnet, and a magnet, which is rotated in 

 one direction by one pole and in the opposite direction by the other, 

 we have the means of still further exploring this curious action of a 

 magnet on a distant bar of iron or steel, and I ask your special atten- 

 tion while I make the following experiments, which give additional 

 evidence of the power of this noble instrument, for it alone can 

 accomplish what I now proceed to show you. 



In my hands I hold a piece of gas-pipe, which I have carefully 

 freed from any trace of magnetism, by a process which you will pres- 

 ently appreciate. You see that it is really devoid of magnetism, for 

 you observe that when it is brought close to, and pointing toward, the 

 center of the lantern needle it does not produce in it the slightest 

 rotation. I now set in motion the great magnet, and carefully carry 

 this pipe to a distance of about twelve feet from one of its ends, and 

 I point the tube in an east and west line toward its pole ; I now bring 

 the tube again opposite the lantern needle, but, as before, no rotation 

 takes place. I again place myself at the same distance, but, while the 



* This experiment, which appears to have all the beauty of simplicity and completeness, is due to 

 Mr. W. E. Geyer, of Hoboken. 



