MAGNETISM. 



43 



magnetic power. He then had recourse 

 to other methods, of which we are pre- 

 sently to speak, for still further increas- 

 ing: their power, till they were saturated 

 with magnetism. 



(173.) It may here be remarked, that 

 in this, as well as in every other method 

 for procuring artificial magnets, we ad- 

 vance only by successive steps, gaining 

 a little additional power by each suc- 

 cessful process, and employing that 

 which has been acquired by one bar 

 in contributing to the increase of 

 the power of another; while this in 

 its turn gives us the means of re- 

 acting upon the first. This we are 

 enabled to do in consequence of the re- 

 markable circumstance'attending the in- 

 duction of magnetism, and to which we 

 have already adverted ($23), namely, 

 that the power of the magnet which ex- 

 cites magnetism in another body, is it- 

 self increased, instead of being diminish- 

 ed, by such excitation. Hence, by pro- 

 per management, the power of the;seve- 

 ral parts of the apparatus is capable of 

 continual increase, limited only by 

 their capacity for receiving and retain- 

 ing magnetism. 



(174.) After having in this way mag- 

 netized, by the help of terrestrial mag- 

 netism, a certain number of steel bars, 

 we may proceed with them in imparting 

 magnetism to others ; and being thus 

 provided with a stronger power, may, in 

 our subsequent operations, dispense 

 with that which we had at first em- 

 ployed. 



3. Method by simple Juxtaposition. 



(175.) Simple induction by juxtapo- 

 sition with one or more powerful mag- 

 nets may suffice for the impregnation of 

 very small magnets. But, for this pur- 

 pose, it is not sufficient to place the latter 

 in contact with one of the poles of a 

 magnet, in the manner represented in 

 the following figure (fig. 42) ; be- 



cause, although the small bar or needle 

 becomes magnetic by remaining a suffi- 

 cient time subjected to the influence of 

 the large magnet, yet we find that its 

 two ends do not exhibit a magnetism of 

 equal strength. That which has been in 

 contact with the magnet appears to be 

 the most powerful, in consequence of its 

 magnetism being more concentrated at 

 the very extremity ; while in the re- 



moter end it is more diffused and there- 

 fore less energetic. This inequality is 

 in a great measure remedied by em- 

 ploying two magnets of as nearly equal 

 power as possible, with their dissimilar 

 poles fronting each other, and 'placing 

 the needle to be magnetized in a lint- 

 bet ween them; as shown in fig. 43. 



Fig. 43. 



The effect of such a combination is 

 always more than twice as great as 

 that of each of the magnets when em- 

 ployed singly. It is difficult, however, 

 even with every precaution, always to 

 avoid the superinduction of consecutive 

 poles in the intermediate parts of the 

 needle. 



(176.) The principle we have already 

 referred to, of the increase of power 

 which a magnet acquires by inducing 

 magnetism on other bodies, may here 

 again be applied in augmenting the in- 

 fluence of the magnets we employ in the 

 preceding case. " If a long bar of soft 

 iron be applied to each of the poles of 

 these magnets which are most distant 

 from the needle to be subjected to their 

 action, the power of the magnets will be 

 greatly augmented. A more' convenient, 

 and perhaps equally efficacious method, 

 is to place the magnets A and B, parallel 

 to each other (y?o-.44), while the small 



Fig. 44. 



bar C, to be magnetized, is in contact 

 with the two dissimilar poles at one 

 end ; and to unite those at the other 

 end by a bar of soft iron, R. This bar 

 becomes strongly magnetical by the 

 joint induction of both the magnets, and 

 the magnetism it thus acquires reacts 

 powerfully in strengthening the magnets 

 themselves ; and the needle which con- 

 nects their other poles participates in 

 this augmentation of effect. These 

 auxiliary pieces of soft iron, which serve 

 to retain and conc-entrate the magnetism 

 of steel bars, are;- 1 ailed armatures. 



(177.) Were thi theory of ^Epinus, in 

 its original form, perfectly correct, no- 

 thing more would be required for im- 

 pregnating steel bars with all the mag- 

 netism they are capable of receiving, than 

 following the methods we have now 



