152 Transactions of the American Institute. 



tube is pointing toward the pole, and in the same direction as before, 

 I strike it with this hammer ; the tube rings at the blow, and all of its 

 particles are powerfully agitated. I now present the tube to the 

 lantern needle, and see ! how it swings around. The large magnet 

 really magnetized this tube when I previously pointed it toward its 

 pole ; but only temporarily, the magnetism disappearing as I removed 

 from it. But, when the bar, in exactly the same position, was vibrated 

 by the blow, it received a permanent charge. Thence we deduce 

 another important fact, namely, that to produce at a distance from a 

 magnet a permanent magnetic charge in a bar of iron (or steel) this 

 must not only point toward its pole, but also its particles must be vio- 

 lently shaken. 



By these conclusive experiments, we see that it is not necessary for 

 an iron or steel bar to touch a magnet to derive from it either a tem- 

 porary or a permanent magnetic charge, for, at a distance of twelve 

 feet, we have shown that the magnet influences the iron, or induces it 

 to become a magnet like itself ; hence, this action of a magnet on a 

 distant mass of iron or steel is called induction. 



It now only remains to examine how the poles of these induced 

 magnets are situate when referred to the positions of the poles of the 

 inducing magnet. In the last experiment you observed that I pointed 

 toward the great magnet the red end of this iron tube, and that on 

 presenting this end to the center of the lantern needle you saw its 

 spear or north end rotate toward it. I again repeat the experiment ; 

 you see it is as I say. Therefore this direction of rotation tells us that 

 this red end of the bar is a south magnetic pole, and you observe that 

 the other, or white end, is a north pole, because, as you see, it produces 

 in the needle a rotation in the opposite direction. Now we will 

 examine the magnetic condition of the end of the great magnet 

 toward which the bar pointed, and then we can deduce another of 

 those general rules, or laws, which are to serve us in our demonstra- 

 tion. 



Here, on this w T ooden column, is a magnetic bar, over two feet long, 

 which you observe turns freely on a hard steel point. It, therefore, 

 has placed its length in the magnetic meridian, and on this end, 

 which points toward the north, I have tied this ball of red cotton- 

 wool. I will now carry this column near that end of the great magnet 

 toward which we pointed the iron tube, and placing on the steel point 

 the magnetic bar, you all observe that the cotton-wool moves away 

 from the magnet ; therefore, this end of the magnet is its north pole. 

 From these facts we can deduce this general rule : When a bar of 



