Scientific Lectures. 157 



latitude twenty-nine degrees twenty-five seconds south and thirteen 

 degrees ten seconds west, from the meridian of the Lizard, the south 

 point the needle respected the upper end of the iron and the north 

 point of the lower end strongly." The sailor's evidence is completely 

 in our favor, and especially will it so appear when you refer to any 

 physical chart of the globe, where you will find that latitude eight 

 degrees seventeen seconds south and longitude seventeen degrees 

 thirty-five seconds west of the Lizard is almost exactly on that line 

 laid down as the magnetic ecpiator, on which the inductive actions of 

 the north and south poles neutralized each other. 



The first series of experiments we made on the distant action of the 

 great electro-magnet suggested these, which we have so successfully 

 repeated with the earth ; but you will recall other experiments, in 

 which a bar of rather hard iron pointing toward the pole of that 

 magnet was permanently magnetized, when in that position I made it 

 ring with the blow of a hammer; whereas when gently removed from 

 that position, without having been agitated, it was found to be 

 unmagnetized. Let us repeat these experiments, for all the condi- 

 tions of their manifestation are known and can readily be obtained 

 with the earth. Holding this bar horizontally with either end near 

 the center of the lantern needle, you see that it is free of magnetism, 

 for the needle does not move. I now place its length parallel to the 

 direction of those stretched cords ; this condition seems exactly 

 to correspond to our previous experiment, when at a distance of 

 twelve feet we pointed a bar toward the pole of the large magnet. 

 1 now bring it into a horizontal position, and again place its end near 

 the center of the needle ; you see it is still unmagnetized, exactly as 

 when, after pointing a bar toward the magnet, we brought it near 

 this needle. But we found that it was permanently magnetized when, 

 in that position, its molecules were powerfully vibrated. This con- 

 dition we can readily fulfill. Observe, I place the red end of the bar 

 down, with its length parallel to those stretched cords, and now I 

 strike down on its upper end with this hammer. We will hold it in 

 the same position until its ring has died away. ISTow it has ceased to 

 tremble ; and placing it again in a horizontal position, I bring its red 

 end near the needle. You all see how violently the needle swings 

 around, its spear, or north end, rushing away from the bar, showing 

 that the red or lower end has received a charge of north magnetism. 

 The upper, or white end, is now opposite the center of the needle, 

 and you see that it is as powerfully charged with south magnetism. 

 The experiment is a beautiful one, but we have not yet seen all of 



