Scientific Lectures. 155 



those conditions necessary for the earth to act on it do not yet exist, 

 for the bar must point toward the assumed position of its magnetic 

 pole. I will, therefore, presently slowly raise this bar until its length 

 is parallel to those stretched lines, and then, if the earth be a magnet, 

 the needle should not only rotate, but the spear-end of it should go 

 away from the lower end of the bar ; and also if the rod, retaining its 

 direction, should be lowered in the direction of its length, until the 

 center of the bar has come opposite the needle, then the latter should 

 return to the position it had when the bar was away ; and, farther- 

 more, on lowering yet more the bar until its upper end comes oppo- 

 site the needle, we should see it again rotate, but this time its spear- 

 end should approach the iron bar. 1 am now slowly elevating this 

 white end of the bar, while the other, or red end, remains near the 

 needle ; see, it really is turning on its center, and the spear-end, as 

 we imagined, is moving away from the rod. I have now brought 

 the length of the rod parallel to the stretched cords, and observe how 

 powerfully the needle is deflected, the spear-end turned away from 

 the rod. I will now lower the rod along the line of its length ; you 

 observe the needle slowly moving to the position it had before the 

 iron bar was brought near it, and now it is steady at that position, 

 and the center of the rod is opposite the needle. I lower it yet 

 further, and the needle is now turning in the other direction, the 

 spear-end is approaching the bar, and now it has come quite close to 

 it, and the upper, or white end of the bar, is opposite the center of 

 the needle. I now reverse the position of the bar, and place the red end 

 up ; the white end is now close to the needle, and see, how the latter 

 is swinging away from it. This white end has now north polarity, 

 the same as the red end had when it was similarly placed. On lower- 

 ing the bar in the line of its length, you see that its center is again 

 devoid of action on the needle, and now that its upper or red end is 

 opposite the needle, you observe the spear-end of the needle quite 

 close to it, showing that again the upper end is of south magnetic 

 polarity. I now remove the rod, and placing it in a horizontal posi- 

 tion, I bring either end near the needle's center; you see that its 

 magnetism has left it. From all of these experiments what are we to 

 infer ? That the magnetism of a bar of soft iron depends alone on 

 its position, and is, therefore, due to some action outside of itself. 

 When placed in a horizontal east and west line it is devoid of all 

 magnetic properties ; when placed parallel to these cords it is power- 

 fully magnetic, and also, whichever end is downward that end has 

 north magnetism. Thus have we found really existing in nature 



