Scientific Lectures. ]49 



any magnetized bar of steel can freely turn on its center, it will (here 

 in New York) place its length in a northerly and southerly line. 



We will now reverse our first experiments, and, instead of allowing 

 a fixed magnet to act on movable masses of iron, we will see what 

 takes place when a fixed mass of iron acts upon a movable magnet. I 

 take this short piece of soft iron and point it toward the spear-end of 

 the needle ; you see that the spear moves toward it. I now bring it 

 opposite the other end of the needle, and it also moves toward the 

 iron. The iron pulls to itself, indifferently, either end of the needle. 

 Hence, if a rod of iron be placed at right angles to the length of a 

 magnetic needle, and point toward its center, the needle will not 

 rotate. You see this deduction is correct, for there, in the bright cir- 

 cle, you see the iron rod pointing toward the center of the needle and 

 the spear-end remains steady at thirty-five degrees.* 



Let us now see what action this other magnetic needle will have 

 on the similar one in the lantern. We have seen that the spear-end 

 of each pointed in the same direction. I bring these two ends oppo- 

 site each other. How remarkable ! the spear-end of the lantern 

 needle is repelled. Heretofore all of our phenomena were facts of 

 attraction ; here we first meet with repulsion. The swinging needle 

 is now rapidly coming back to its thirty-five degree point, and 1 will 

 again bring the same end of the needle close to it ; see, although it 

 was coming back to its position of preference with a rush, yet the 

 repulsive action between the similar ends of these magnets is such 

 that the swing of the needle was not only arrested, but its motion was 

 reversed. See, again, how it shies away as I again bring the spears 

 near each other. But attraction also exists between these magnets, 

 as you perceive, as I bring the other end of this needle to point 

 toward the spear-end of the lantern needle. Rapidly it swings 

 toward it, and I had to be very quick in my movements or the unlike 

 ends would have struck together. To bring forcibly before you the 

 differences in the action of the iron and of the magnet on the same 

 needle, I now, as I did with the iron, place the magnet at right 

 angles to the length of the magnetic needle, and pointing toward its 

 center. The needle now, however, does not remain steady at thirty- 

 five degrees ; it rotates ; the spear-end of the stationary magnet draws 

 to itself the other end of the needle. I reverse the position of the 

 magnet, and the direction of rotation of the needle is also reversed. 



* The pointing of the needle to this particular division means nothing, for the graduated plate was 

 placed on the lantern without thought as to the direction of the zero point, and it merely happened 

 that the needle pointed to thirty-five degrees when it came into the magnetic meridian. 



