On the transient magnetic state of which various substances are susceptible / [Sir W. Snow Harris].

  • Harris, W. Snow (William Snow), Sir, 1791-1867
Date:
1831
Catalogue details

Licence: Public Domain Mark

Credit: On the transient magnetic state of which various substances are susceptible / [Sir W. Snow Harris]. Source: Wellcome Collection.

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    magnet to the similar pole of a very weak one, this new distribution can be effected, an attractive force immediately follows. 35. There are some circumstances connected with this curious result of mag- netic action, which seem to apply immediately to the question under consi- deration, but which have not been generally observed. If two similar mag- netic poles of very unequal force be opposed to each other, the greatest repul- sion, taking into account the difference in distance, will be a little within the limit of their action: that is to say, the increments in the repulsive energy are comparatively less, as the magnets approach each other: evidently resulting from the change which begins to take place in the magnetism of the bars. Now if one of the bars be extremely powerful in regard to the other, the new distribution in the weaker bar is effected even before the point of contact. The precise point at which the existing polarity of the weaker bar becomes changed varies with the force of the stronger magnet. This point may be found by experiment in the following way. Let a small cylindrical magnet be suspended by a silk line from a delicate wheel, whose axis rests on friction rollers; and let it be counterpoised by a small weight at the extremity of a short cylin- drical piece of wood partly immersed in a jar of water. If one pole of a power- ful bar be now carefully approximated towards the like pole of the suspended magnet, by fixing the former in a brass frame carrying a micrometer-screw, the latter will be observed to recede from the bar, until the opposed poles are within a certain distance of each other; when the repulsion will cease, and a weak attractive effect ensue. The cylinder of wood as it becomes gradually immersed *, continually furnishes an equivalent to the repulsion, in the quan- tity of water displaced. We do not generally perceive the attractive effect resulting from this induc- tive action in non-ferruginous masses; for, as already observed, their feeble retentive power admits of the magnetic neutrality being more rapidly restored, when the tension passes a certain point. So that in fact, the opposite magnetic state never becomes sufficiently intense to evince an attractive force, cogni- zable by the ordinary means. * A more detailed account of this experiment may be found in the Transactions of the Royal Society of Edinburgh.