Scientific Lectures. 159 



I think we can say that the experiments we have made with these 

 magnets have well directed ns in the progress of our experimental 

 solution of the problem of the earth's magnetism ; and this encour- 

 ages me to examine more minutely the manner in which these curious 

 attractive and repulsive effects, which we call magnetism, are distri- 

 buted over the surface of these magnetic bars. We can only thus hope 

 to secure more light to illumine our further progress, which seems here 

 almost brought to a termination. But from experience we know 

 that it is generally only by the most searching look into known 

 phenomena that we can obtain that dim view of the path which leads 

 to the hidden truths beyond, and thus, therefore, we will endeavor to 

 find an opening into further research. 



"We have, as yet, only examined roughly the effects of the ends 

 and of the central portions of a magnet on bars of iron; but we can, 

 instead of using these large bars and needles, make use of quite 

 minute and very short bars in the form of iron filings, and by this 

 process give many points for the magnetic radiation to act on ; and 

 by distributing these points over the whole surface of the magnet 

 we may arrive at some highly suggestive results. The idea is worth 

 following up and we will proceed to test its value. 



I strew this glass plate with finely sieved filings made from the 

 softest Norway iron, which has been repeatedly annealed, and I place 

 it over the horizontal lens of the vertical-lantern, and I lay this small 

 bar magnet on the filings. You observe how they arrange. them- 

 selves about its ends. I now roll the bar over and over, and you see 

 more evidently than before that the attraction is localized. The 

 middle of the bar has no filings adhering to it, but observe from the 

 ends of the magnet these radiating iron filaments, and remark how 

 their gradually declining contour actually shows the magnetic hold 

 on the iron gradually diminishing from near the ends of the magnet 

 toward its center. 



I now modify this method of exploring the distribution of the 

 magnetic force. I place this same bar magnet on the condensing 

 lens of the lantern, and down on it I lower this glass plate on which 

 has been sifted iron filings. They do not appear in the least affected 

 by the magnet beneath them ; but, observe when I let fall vertically 

 on the plate this piece of light copper wire ; see the curious lines 

 that are growing around the magnet. These, proceeding outward 

 from the ends appearing to radiate like rays of light from points 

 within which we call the poles, while these, originating nearer its 

 center, bend over the magnet, and in graceful curves embrace it. 



