MAGNETISM. 37 



but my object was to ascertain whether they would act on each 

 other, with this view, I suspended one of the bars by a long and 

 slender thread, the bar being inclined to the horizon to about 

 80**, was allowed to settle at rest, I then applied the lower end 

 of the bar I held in my hand, to the upper end of the one sus- 

 pended by the thread, and I found that an attractive force exis- 

 ted between them ; I then applied the upper end of the bar held 

 in the hand, to the upper end of the suspended bar, when a re- 

 pulsion took place : by changing the bars in every possible way, 

 I found that I could put 18 cubic inches of iron in motion, 

 either by attraction or repulsion, to the right or left, and that 

 these two bars of soft iron had all the properties of real magnets, 

 by induction from terrestial magnetism. I suspended the bars 

 nearly in an horizontal position, when they invariably rested, 

 either in the direction of the magnetic needle, or else veri/ near it. 



Now the attractions found as above cannot be classed with that 

 force which holds the component parts of our earth together, and 

 by which all its parts gravitate as to a common centre, but 

 must be regarded as magnetic attraction as well as repulsion, and 

 consequently polarity, so clearly developed in these experiments. 

 Any person may satisfy himself of the truth of my assertion by 

 making similar experiments on soft iron. 



Soft iron is therefore magnetical and polarized with respect to 

 position, with the earth's axis, and will either attract or repel 

 the compass needle, according to the distance and position of the 

 respective poles, and since ships are steered by a rudder fixed at 

 the stern, it is necessary that the compass should be near the 

 stern also, and on the upper deck, so that the compass is necessa- 

 rily placed abcift, and above the greatest part of the iron in a ship : 

 and, since the upper part of each particle of soft iron is a south 

 pole, (in north magnetic latitude) and attracts the north point of 

 the compass needle : while the lower part of each article of iron 

 attracts the south point of the compass, and repels the north point, 

 it follows that the compass being above and abaft the greatest 

 part of the iron on board, its north point is nearest the upper 

 part (south poles) of all the iron before it, and the force of mag- 

 netic attraction, being inversely as the square of the distance, 

 the north point of the compass will be drawn forward by the 

 local attraction of the guns, tanks, anchors, iron knees, ballast, 

 &c., so that, in north magnetic latitude, a ship is liable to be 

 to the southward of the course indicated by the compass, whe- 

 ther her course be towards the east or west. 



