the Lines of Magnetic Force. 427 



3297. With regard to the great point under consideration, it 

 is simply, whether the lines of magnetic force have a physical 

 existence or not ? Such a point may be investigated, perhaps 

 even satisfactorily, without our being able to go into the further 

 questions of how they account for magnetic attraction and repul- 

 sion, or even by what condition of space, aether or matter, these 

 lines consist. If the extremities of a straight bar-magnet, or if 

 the polarities of a circular plate of steel (3274.), are in magnetic 

 relation to each other externally (3257.), then I think the exist- 

 ence of curved lines of magnetic force must be conceded (3258. 

 3263.)* ; and if that be granted, then I think that the physical 

 nature of the lines must be granted also. If the external rela- 

 tion of the poles or polarity is denied, then, as it appears to me, 

 the internal relation must be denied also ; and with it a vast 

 number of old and new facts (3070. &c.) will be left without 

 either theory, hypothesis, or even a vague supposition to explain 

 them. 



3298. Perhaps both magnetic attraction and repulsion, in all 

 forms and cases, resolve themselves into the differential action 

 (2757.) of the magnets and substances which occupy space, and 

 modify its magnetic power. A magnet first originates lines of 

 magnetic force; and then, if present with another magnet, offers in 

 one position a very free conduction of the new lines, like a para- 

 magnetic body; or if restrained in the contrary position, resists 

 their passage, and resembles a highly diamagnetic substance. So, 

 then, a source of magnetic lines being present, and also magnets or 

 other bodies affecting and varying the conducting power of space, 

 those bodies which can convey onwards the most force, may tend, 

 by differential actions, with the others present, to take up the 

 position in which they can do so the most freely, whether it is 

 by pointing or by approximation ; the best conductor passing to 

 the place of strongest action (2757.), whilst the worst retreats 

 from it, and so the effects both of attraction and repulsion be 

 produced. The tendency of the lines of magnetic force to shorten 

 (3266. 3280.) would be consistent with such a notion. The 

 result would occur whether the physical lines of force were sup- 

 posed to consist in a dynamic or a static state (3269.). 



3299. Having applied the term line of magnetic force to an 

 abstract idea, which I believe represents accurately the nature, 

 condition, direction, and comparative amount of the magnetic 

 forces, without reference to any physical condition of the force, 

 I have now applied the term physical line of force to include the 

 farther idea of their physical nature. The first set of lines I 

 affirm upon the evidence 'of strict experiment (3071, &c.). The 



* Sec for a caie of curved lines the inclosed and compressed system of 

 forces belonging to the central circular magnet, flgi 6 (.5275.). 



