VOL. XLIV.] PHILOSOPHICAL TRANSACTIONS. 3Q5 



pole to the other internally, and is then carried back in curve lines externally, 

 till it arrives again at the pole where it first entered, to be again admitted. 



Exper. 1 . — If we lay a magnetical body under a piece of paper or glass, that 

 is strewed over with steel filings or magnetical sand, and by striking the table put 

 the filings in motion, they will readily dispose themselves in such a manner as to 

 represent, with great exactness, the course of the magnetic matter. Steel ren- 

 dered magnetical is best for this purpose, because it is of a more uniform tex- 

 ture than loadstones, and will on that account exhibit a more regular appearance. 

 By this experiment the curve lines in which the magnetical matter returns back 

 to the pole where it first entered are accurately expressed by the arrangement of 

 the filings. The largest curves are such as take their rise from one polar sur- 

 face, and are extended to the other ; being larger in proportion as they arise 

 nearer the axis or centre of the polar surface. Those curves which arise from 

 the sides of a magnetical body are always interior to those which arise from the 

 polar surface ; and are less and less in proportion to their distance from the ends. 

 If any one should doubt whether the magnetical matter, which thus disposes the 

 filings, is really moving back in a direction contrary to that with which it passes 

 through the magnetical body, let him try it in different parts with a small com- 

 pass needle, and the fact will appear beyond dispute. 



Exper. 2. — ^The larger the distance is from pole to pole in different magnets, 

 the larger will these cui-ves be. This appears from examining magnets of dif- 

 ferent lengths. And this is the reason why, in the same magnet, the curves are 

 less in proportion to their greater distance from the ends of the bars. P'or the 

 poles from whence these curves arise are proportionably nearer each other. 



Exper. 3. — If the south pole of one magnet be opposed to the north of an- 

 other, most of the magnetic matter is carried directly out of one into the other : 

 and does not return back in curve lines till after having passed through both 

 magnets. It appears from the arrangement of the filings, that the magnetic 

 matter proceeding from the polar surface, does not now diverge from the axis as 

 before, but runs more in straight lines, till it arrives at the polar surface of the 

 other magnet. The curves arising from the sides, which before were bent to^ 

 wards the opposite end of the same magnet, ai-e many of them now bent the 

 contrary way, towards the corresponding sides of the other magnet. Those 

 which are not bent the contrary way, are such as are too remote from the op- 

 posed pole of the other magnet to be influenced by it ; and therefore continue 

 their natural course. 



Exper. 4. — While the bars are in the position of the last experiment, if a 

 small loadstone Ije placed in the stream running from one to the other, in any 

 position whatever, the stream will pass through the stone : which, being again 

 removed, will be found to have a polarity exactly in the direction of that stream. 



3 E 2 



