and Phenomena of Magnetic Induction. 261 



Whilst these striking results were obtained by the action of 

 the end of the bar nearest to the magnets, the influence at the 

 distant end was but feeble — sustaining only nails of 20 grains, 

 and 37 grains, at the two last distances of the third column. 



In experiments merely illustrative of the power of induction, 

 the arrangement of the last column of the table may be still 

 farther improved by raising the bar so high that the lower ex- 

 tremity of the suspended substance may be on the same hori- 

 zontal level as the magnets. In this position the lower extre- 

 mity of the nail being nearest to the magnets, becomes a south 

 pole, with a north pole, by consequence, at the upper end, 

 which, being attractable by the southern polarity induced in the 

 bar, augments its suspensive power. And such was the increase 

 obtained by experiment, that the nail of 482 grains was now 

 suspended (by either end of the bar, when presented in succes- 

 sion to the magnet), at the distance of nine inches, and the key 

 at the distance of 7.2 inches, the interval between the bar and 

 the magnets. 



Subsequent experiments were made with a flat iron bar, a 

 quarter of an inch in thickness, but similar in all its other di- 

 mensions and quality to the bar previously employed. The 

 distances of suspension obtained by this bar, indicated a smaller 

 quantity of inductive influence, corresponding pretty nearly with 

 its proportion of surface. 



These, however, are but proximate results: the inductive ef- 

 fect as measured by the deviations produced on the needle of a 

 compass was therefore resorted to for a more satisfactory ratio. 



The apparatus employed in this investigation consisted of 

 four similar bar-magnets, each 13} inches long, 1 inch broad, 

 and Jth of an inch thick ; the square bar of soft iron used in the 

 foregoing experiments, being of the same length and breadth as 

 the magnets ; and a delicate compass of four inches diameter. 

 The magnets were placed parallel to each other on a board, half 

 an inch asunder, in order both that their combined influence 

 might be employed for affording more decisive results, and that 

 they might be presented at different distances from the bar in the 

 same relative position and equality of magnetic power. The iron 

 bar was placed in a horizontal position, in the first instance be- 

 twixt the magnets and the compass, and in an east and west 



