the Laws of Magnetic Forces. 317 



magnetic centre ; and this law can always be made apparent in 

 a bar of steel regularly hardened and magnetized throughout. 

 The results, however, are by no means certain in bars whose tem- 

 perament and texture is irregular, or which are only hardened 

 at the extremities : in the one case the magnetism is irregularly 

 retained, in the other it is only sensible at the poles of the bar. 



52. In order to avoid the interference of the angular forces to 

 a still greater extent, so as to have the action reduced as far as 

 possible to that of an isolated point, the attractive force was 

 made to operate through a small cylindrical piece of iron, about 

 two inches long, a b, Fig. 18. Thus, the suspended iron x was 

 preserved always without the influence of the bar. In this case, 

 we may suppose, from what has been before shewn respecting 

 magnets by induction, that, in consequence of the other points 

 of the bar acting at angular distances upon the cylindrical mass 

 of iron ab, the induced force arising from these points would, in 

 certain cases, not exert a sensible influence on its distant extre- 

 mity ; and thus the attractive force by induction would approxi- 

 mate very closely to that resulting from the point b of the mag- 

 net in contact with the iron, which would thus, compared with 

 the other points acting at a distance, and under different 

 angles, be very great, whilst a fair measure would still be ob- 

 tained of the magnetic intensity ; for we have already seen 

 (29), that the masses of iron under the influence of a magnet 

 generally exhibit, at their distant extremities, an attractive force 

 directly proportionate to the magnetic intensities, all other 

 things remaining the same. Now, the successive points of a 

 magnetic bar between the centre and poles, may be considered 

 as so many distinct magnets, varying in intensity : the inductive 

 effect on the iron in contact with them is, therefore, a fair mea- 

 sure of their force. In the following Table are given the results 

 of a series of experiments thus arranged : the magnetic bar be- 



RT 2 



