1 76 On the Molecular Movements and Magnetic Changes in Iron, 



full heat of five small Bunsen's burners, in about four minutes 

 the needles were rather suddenly deflected 2|° with irregular 

 action at a particular temperature not even approaching that of 

 the lowest visible redness in the dark ; and by heating to a much 

 higher temperature, but still below redness, faint signs of a 

 second similar molecular disturbance in the same direction were 

 manifested. The heat being now stopped and the bar allowed 

 to cool gradually, the same phenomena, and to the same extent, 

 took place, but in an exactly reverse order. On repeating the 

 experiment with this bar, but cooling the bar rapidly by conti- 

 nuous application of cold water, a sudden deflection of 8° oc- 

 curred when the bar acquired the proper temperature. The 

 direction of all the deflections with this bar (as with nearly all 

 the previous bars) during heating agreed with those producible 

 by a decrease of magnetism, and during cooling with an increase 

 of magnetism. By substituting for the fine-wire coil another, 

 containing 3600 turns of size " No. 29 " ( = 028 millim. thick) 

 copper wire, very feeble results only were obtained, the coil itself 

 offering too great a degree of conduction-resistance. 



In these experiments with wrought iron, steel, cast iron, and 

 nickel there is a very gradual magnetic change, in addition to the 

 several sudden or irregular molecular movements and changes of 

 magnetism ; this gradual change is manifested by a very faint 

 deflection of the needles in the same direction as those produced 

 by most of the sudden movements. 



By substituting a bar of zinc 3 feet ( = 91 centims.) long and 

 1 inch ( = 25*4 millims.) thick, or one of antimony 30 inches 

 ( = 76*2 centims.) long and 1 inch thick, for those of the other 

 metals, and heating their middle parts to incipient fusion, I ob- 

 tained no definite movements of the galvanometer-needles. With 

 a bar of bismuth 15 inches ( = 38*1 centims.) long and about 

 \ an inch ( = 12*7 millims.) thick, and heating its middle part, 

 also no movements of the needles took place. 



With a bar 9 inches ( = 23 centims.) long and 2 J inches 

 ( = 6'3 centims.) thick, composed of commercial antimony con- 

 taining a small amount of iron, and with suitable coils about 1^ 

 inch ( = 3'8 centims.) in length upon its ends, an irregular suc- 

 cession of ten distinct internal changes in the bar, corresponding 

 to decreases of magnetism, were observed during the heating. 

 The bar was then so hot as to char the wooden wheels contain- 

 ing the wire, and had to be cooled ; during its cooling a continued 

 succession of changes of an opposite kind took place. With a 

 second bar 13 inches* ( = 33 centims.) long and 1^ inch ( = 3'8 

 centims.) thick, containing more iron, the effects were very 

 feeble, chiefly owing to the wire coils being much further asunder. 



The method I have adopted admits of the detection of minute 



