34G On the anomalous JMagnetic Acl/ott 



In our first exjierinicnt, (he compass was jilaccd nearly west 

 of the bar, rather below its u})iicv extreiiiity, and distant from 

 it about 6i inches. At the white heat the attraction of the 

 iron was lost; and at the blood-red heat we had 70° of de- 

 viation in the needle ; but that intermediate action we were 

 searching after did not appear ; at least it was by no means 

 so obvious as we had noticed it in our preceding experi- 

 ments. 



The position of the bar and compass was not however quite 

 the same as before; we therefore raised the support of the bar 

 about four inches, by which means its U})per extremity was 

 the same height above the compass ; and on repeating the ex- 

 periment with the bar thus placed, we obtained an obvious 

 deviation of the south end of the needle towards the iron of 

 4i°, which remained fixed about two minutes. 



Having gained this by raising the bar four inches, we now 

 raised it six inches ; and on applying it in this place, we ob- 

 tained a deviation of 10i°, which remained fixed about the 

 same time as before ; when the needle suddenly yielded to the 

 natural magnetic power of the iron, and obtained almost in- 

 stantaneously a deviation of 81° the opposite way. 



It was thus rendered obvious, that the quantity of negative 

 attraction at the red heat, depended upon the height or depth 

 of the centre of the bar from the compass; and as the natural 

 effect of the cold iron v.as changed by placing the compass 

 below the centre of the bar, the question which naturally sug- 

 gested itself was. Will the negative attraction also change? 

 To decide this point, we lowered our compass to within six 

 inches of the bottom of the bar; in which position the cold 

 iron necessarily attracted the south end of the needle, and 

 produced a deviation of 21°. Upon heating the bar, wc found, 

 as usual, all its power upon the needle cease at the white 

 heat; but as this subsided into the bright red, tlie negative 

 attraction began to manifest itself, and it soon amounted to 

 10^°; the north end of the needle being attracted towards llie 

 iron. Here it I'emaincd stationary a short time, and then 

 gradually returned, first due north, and ultimately to 70° '30' 

 on the opposite side. 



Having made these preliminary experiments, I was anxious 

 to undertake a regular series, hoping by this means to be able 

 to reduce this species of action to some fixed principle ; for it 

 will have been observed, from what is stated above, that the 

 negative attraction appeared to increase from each extremity 

 of the bar towards its middle; whereas the positive or natural 



action 



