292 Mr HARRIS'S Experimental Inquiries concerning 



so very small, as to leave no doubt concerning the law we have 

 endeavoured to investigate. It will, however, be necessary to 

 remember, that, in these experiments, we have not examined the 

 absolute attractive force exerted between a mass of iron and a 

 magnet, at different distances, but merely the law of the influ- 

 ence of a magnet upon a mass of unmagnetized iron, so as to in- 

 duce in it a development of magnetic action. 



24. This simple law of magnetic induction is observed to pro- 

 ceed uniformly from the distance at which the force first becomes 

 measurable, until the iron and magnet are very nearly approxima- 

 ted, but then begins to vary. Thus, in the preceding experiments 

 (19. 23), when the iron and magnet were approximated within 

 the tenth of an inch, the increments in the attractive force be- 

 gan to diminish. It would appear from this circumstance, either 

 that the similar and distant polarities begin in this case to exert 

 a sensible influence in disturbing the result, or that a limit ex- 

 ists, approaching saturation, beyond which the inductive effect 

 on the iron does not proceed with the same facility as before. In 

 either case, this limit may be supposed to vary with the power 

 of the magnet. This was made evident by employing magnets 

 of different degrees of intensity in succession. Thus, it was ob- 

 served, that, although the induced effects on a mass of iron 

 were at first respectively proportional to the powers of the mag- 

 nets, yet the increments in the attractive force acquired by 

 approximation began to diminish at a greater or less distance 

 from the magnet, according as the original magnetic force was of 

 greater or less intensity. 



25. The attractive force of magnets by induction at their dis- 

 tant poles is, all other things remaining the same, inversely pro- 

 portional to the lengths of the iron, and, as just observed, at 



