the Lines of Magnetic Force. 421 



of the external lines to the lines of force within the magnet. In 

 the same way the armature of a natural loadstone is useful. All 

 these eifects and expedients accord with the view, that the space 

 or medium external to the magnet is as important to its exist- 

 ence as the body of the magnet itself. 



3285. Magnets, whether large or small, may be supersaturated, 

 and then they fall in power when left to themselves ; quickly at 

 first if strongly supersaturated, and more slowly afterwards. This, 

 upon the hypothesis, would be accounted for by considering the 

 surrounding medium as uuable, by its feeble magneto-conducting 

 power, to sustain the higher state of charge. If the conducting 

 power were increased sufficiently, then the magnet would not be 

 supersaturated, and its power would not fall. Thus, if a magnet 

 were surrounded by iron, it might easily be made to assume and 

 retain a state of charge, which, if the iron were suddenly replaced 

 by air, would instantly fall. Indeed, magnets can only be su- 

 persaturated by placing them for the time under the dominion 

 of other sources of magnetic power, or of other more favourable 

 surrounding media than that in which they manifest themselves 

 as supersaturated. 



3286. The well-known result, that small bar-magnets are far 

 stronger in proportion to their size than larger similar magnets, 

 harmonizes and sustains that view of the action of the external 

 medium which has now been taken. A sewing-needle can be 

 magnetized far more strongly than a bar twelve inches long and 

 an inch in diameter ; and the reason under the view taken is, 

 that the excited system in the magnet (correspondent to the vol- 

 taic batteiy in the analogy quoted (3276.)) is better sustained 

 by the necessary conjoint action of the surrounding medium in 

 the case of the small magnet. For as the imperfect magneto- 

 conducting power of that medium (or the consequent state of 

 tension into which it is thrown) acts back upon the magnet 

 (3282.), so the smaller the sum of exciting force in the centre 

 of the magnetic sphondyloids, the better able will the surround 

 ing medium be to do its part in sustaining the resultant of force. 

 It is very manifest, that if the twelve-inch bar be conceived of as 

 subdivided into sewing-needles, and these be separated from each 

 other, the whole amount of exciting force acts upon, and is car- 

 ried onwards in closed magnetic curves, by a very much larger 

 amount of external surrounding medium than when they are all 

 accumulated in the single bar. 



3287. The results which have been observed in the relation 

 of length and thickness of a bar-magnet, harmonize with the view 

 of the office of the external medium now urged. If we take a 

 small, well-proportioned, saturated magnet, as a sewing-needle; 

 alone, it has, as just 6tated, such relation to the surrounding 



