the Lines of Magnetic Force. 423 



being able to sustain external lines of force to that amount. But 

 if a third bar, two inches long and also five-tenths in diameter, 

 be magnetized at the same time, it can receive much more power 

 than the second one. A natural i-eason for this presents itself 

 by the hypothesis ; for the limitation of power in the two cases 

 is not in the magnets themselves, but in the external medium. 

 The shorter magnet has contact and connexion with that medium 

 by a certain amount of surface ; and just what power the medium 

 outside that surface can support, the magnet will retain. Make 

 the magnet as long again, and there is far more contact and rela- 

 tion with the surrounding medium than before ; and therefore 

 the power which the magnet can retain is greater. If there were 

 such limited points of resulting action in the magnet as is often 

 understood by the word poles, then such a result could hardly 

 be the case, on nay view of the physical actions. But such poles 

 do not exist. Every part of the surface of the magnet, so to 

 say, is pouring forth externally lines of magnetic force, as may 

 be seen in figs. 2, 3, 4, 5 (3274.). The larger the magnet, to a 

 certain extent, and the larger the amount of external conducting 

 medium in contact with it, the more freely is this transmission 

 made. If the second magnet, being an inch long, be conceived 

 to be charged to its full amount, and then, whilst in free space, 

 could have half an inch of iron added to its length at each end, 

 we see and know that many of the lines of force originally issuing 

 from that part of its surface still left in contact with the air at 

 the equatorial part, would now move internally towards the ends, 

 and issue at a part of the soft iron surface; indicating the 

 manner in which the tension would be relieved by this better 

 conducting medium at the ends, and by increased surface of 

 contact with the surrounding bad conductor of air or space. 

 The thick, short magnet could evidently excite and carry on 

 physical lines of magnetic power far more numerous than those 

 which the space about it can receive and convey from pole to 

 pole ; and the increase in the length of the magnet may go on 

 advantageously, until the increasing sum of power, sustainable 

 by the increasing medium in the circuit, is equal to that which 

 the magnet can sustain or transmit internally ; for all the lines 

 of power, wherever they issue from the magnet, have to pass 

 through its equator; and in this way the equator or thickness 

 of the magnet becomes related to its length. So the advanta- 

 geous increase in length of the bar is limited by the increasing 

 resistance within, and especially at the equator of the bar; and 

 the increase in breadth, by the increasing resistance (for in- 

 creasing powers) of the external surrounding medium (3287.). 



3290. It is vi tv interesting to observe the results obtained 

 when an attempt is made to magnetize, regularly, a thin steel 



