and PJienmnena of Magnetic Induction. 869 



the relative capabilities of iron for induced magnetism, may be 

 employed as a satisfactory test of quality in its several kinds.7,ui 



At small distances from a powerful magnet the inductive 

 energy is very striking, and productive of a number of well 

 known and interesting phenomena. Let a piece of soft iron, 

 for instance, such as a common key, be placed near the extre- 

 mity of a bar-magnet, either in continuation of the same line or 

 inclined to each other at any angle, provided either of the ex- 

 tremities of the key and magnet are the parts nearest to ea^h 

 other, and the key so placed will instantly acquire such a mag- 

 netic condition as to be able to support another smaller key or 

 other portion of iron at either of its extremities. And though the 

 magnet be placed beneath the table, or under a slab of marble 

 or any other solid substance, the inductive influence will be pre- 

 cisely the same, so as the distance and position of the masses 

 are similar. 



But these phenomena, which have usually been observed only, 

 in circumstances of juxtaposition, may be satisfactorily exhibited 

 at considerable distances, as shewn by the following experiment. 



A pair of very fine bar-magnets, 3 feet in length, 9.^ inches 

 in breadth, and ^th of an inch in thickness, being placed over 

 each other, a quarter of an inch asunder, and with similar poles 

 adjacent, were employed, with a view to their inductive effects, 

 at different distances, on the nearest end of a soft bar of square 

 iron, 13| inches long, and 1 inch in thickness. In order that 

 the inductive influence might be separated from any magnetism 

 of position derived from the earth, the iron bar was placed in 

 the east and west magnetic line, and in a horizontal position ; 

 and that the more delicate experiments might not be affected 

 by the magnetism acquired under the more powerful influences, 

 the most distant and weakest inductions were first tried, and 

 each experiment verified by taking^the mean power of each end 

 of the bar alternately presented to the magnets. The iron bar 

 thus situated (Plate II. Fig. 1.) sustained by the extremity 

 nearest to the magnets (when all the points of contact were po- 

 lished) the substances and weights, at the distances respectively 

 annexed to each, as given in the first three columns of the fol- 

 lowing table : — 



