422 Dr. Faraday on the Physical Character of 



space as to have its high condition sustained; if we place a 

 second like magnetic needle by the side of the first, the surround- 

 ing space of the two is scarcely enlarged, it is not at all improved 

 in conducting character, and yet it has to sustain double the in- 

 ternal exciting magnetic force exerted when there was one needle 

 only (3232) ; this must react back upon the magnets, and cause a 

 reduction of their power. The addition of a third needle repeats 

 the effect ; and if we conceive that successive needles are added 

 until the bundle is an inch thick, we bave a result which will 

 illustrate the effect of a thickness too large, and disproportionate 

 to the length. 



3288. On the other hand, if we assume two such needles 

 similarly placed in a right line at a distance from each other, 

 each has its surrounding system of curves occupying a certain 

 amount of space ; if brought together by unlike poles, they form 

 a magnet of double the length ; the external lines of force co- 

 alesce (3226.), those at the faces of contact nearly disappear ; 

 those which proceed from the extreme poles coalesce externally, 

 and form one large outer system of force, the lines of which have 

 a greater length than the corresponding lines of either of the 

 two original needles. Still, by the supposition that the magnets 

 are perfectly hard and invariable, the exciting force within re- 

 mains, or tends to remain the same (3227.) in quantity, there 

 is nothing to increase it. The increase in length, therefore, of 

 the external circuit, which acts as a resisting medium upon the 

 internal action, will tend to diminish the force of the whole 

 system. Such would be the case if a voltaic battery surrounded 

 by distilled water, as the analogous illustration (3276.), could 

 be elongated in the water, and so its poles be removed further 

 apart ; and though in the case of magnets previously charged, 

 some effect equivalent to intensity of excitement may be pro- 

 duced by conjoining several together end on, yet the diminished 

 sustentation of power externally appears to follow as a conse- 

 quence of the increased distance of the extreme poles, or external, 

 mutually dependent parts. Static electric induction also supplies 

 a correspondent and illustrative case. 



3289. The xisual case in which the influence of length and 

 thickness becomes evident, is not, however, always or often that 

 of the juxtaposition of magnets already as highly charged as they 

 can be, but rather that of a bar about to be charged. If two 

 bars, alike in steel, hardness, &c, one an inch long and the tenth 

 of an inch in diameter, and the other of the same length but 

 five-tenths of an inch in diameter, be magnetized to supersatu- 

 ration, the latter, though it contains twenty-five times the steel 

 of the former, will not retain twenty-five times the power, for 

 the reason already given (3287.) ; the surrounding medium not 



