SS Mr Watt on a New Magnetical Instrument, 



attracted by the magnetic fluid, necessarily place itself parallel 

 to the direction of the current of that fluid. 



But this will be still more easily comprehended if we attend 

 to the manner in which magnetism is communicated to a bar of 

 steel ; and we would observe that the general notion, that the 

 poles of a magnet, when used in communicating magnetism to a 

 bar of steel, produce their opposites, is not literally true, as ei- 

 ther the North or the South Pole of the magnet produces al- 

 ways both a North and South Pole. And it depends entirely 

 on what part of the bar, to be rendered magnetic, we first place 

 the pole of the magnet, to determine where any of the poles shall 

 be. If, for example, we place the south poles of two magnets 

 upon the extremities of a bar of steel, and draw them towards 

 the centre of the bar, we render, by a repetition of this ope- 

 ration, both the extremities south poles, or similar to tlie poles 

 used ; and the two north poles will be found at the centre of the 

 bar of steel ; and a needle thus treated will stand east and 

 west, or north and south. And as any single pole of a magnet 

 will communicate both a north and south pole to any bar of 

 iron, the part of the bar it touches first being always a pole si- 

 milar to itself; and the part it is in contact with last, being ne- 

 cessarily of the opposite description ; this seems unfavourable to 

 the idea that there are two magnetic fluids. 



The magnetic fluid simply seems to follow the first direction 

 that is given to it along any piece of steel ; and which can only 

 be changed by drawing a magnet along it in an opposite direc- 

 tion, as almost all our compass needles are rendered magnetic 

 by drawing the north and south poles of two magnets from the 

 centre of the needle to its extremities. Each of our compass 

 needles possess actually four poles ; they have a north and south 

 pole at their centre, and the same at their extremities. 



It is evident, therefore, that the magnetic fluid (or whatever 

 it may be), will run along a bar of steel, in any way it is direct- 

 ed. It will commence at both the extreme points of the bar, 

 and give out at the centre ; or it will commence at the centre, 

 and run off* by the extremities ; and the ends of the same bar 

 may be made both north poles ; or they may be rendered both 

 south; or alternately north and south. 



If this theory of magnetism be correct upon the whole, and 



