1 74 Mr. O. Gore on the Molecular Movements and Magnetic 



at —26° F. (=-32°-2 C.), composed of 4 pounds of ice and 6 

 pounds of crystallized chloride of calcium, an irregular deflection 

 of the needles, indicating another feeble molecular change and 

 increase of magnetism was observed ; the general deflection, how- 

 ever, obtained by this artificial cooling was in accordance with a 

 decrease of magnetism, contrary to that which resulted from cool- 

 ing at higher temperatures : a repetition of this experiment gave 

 similar results. With a bar 3 feet ( = 91*4 centims.) long and 

 1 inch (=25*4 millims.) thick none of the electrical effects were 

 obtained by the heating process, owing to the heat of the gas- 

 burners being not sufficiently powerful. 



These results show that on gradually heating a bar of wrought 

 iron, when it attains a moderate red heat a succession of distinct 

 and separate small movements, all of a similar kind, take place 

 amongst its molecules, — and that on gradually cooling such a 

 heated bar, when its temperature has sunk to moderate redness 

 three successive molecular movements and diminutions of mag- 

 netism occur— the first being a small one, the second a very 

 large movement, and the third also small ; and these movements 

 are all of an opposite character to those which take place during 

 the heating. It is singular that there is no sudden large decrease 

 of magnetism, during the process of heating, to correspond with, 

 the sudden large increase of magnetism during cooling ; and this 

 precisely agrees with the phenomenon of molecular and cohesive 

 change already referred to (page 171). It is probable that the 

 sudden and momentary increase of length and diminution of 

 cohesion which an iron wire under a suitable degree of longitudinal 

 strain undergoes whilst cooling at a moderate red heat, may be 

 due to the sudden great increase of magnetism which it then 

 acquires, in accordance with the fact discovered by Mr. Joule, 

 that a rod of soft iron at 60° F. suddenly increases in length and 

 decreases in diameter when magnetized. 



With a bar of cast steel 27 inches ( = 68*6 centims.) long and 

 \ of an inch ( = 22-2 millims.) in diameter, similarly examined, 

 the fine wire coil containing 2850 turns of "No. 23" ( = 0*7 

 millim. thick) copper wire, the following results were obtained. 

 During heating, a very feeble sudden molecular change, attended 

 by decrease of magnetism, occurred below a visible red heat ; and 

 at a moderate red heat a second sudden, and more extensive, mo- 

 lecular change occurred of the same kind : by further heating to 

 a higher degree of redness no other sudden change took place. 

 The gas-flames being now extinguished, after a period of thirty 

 seconds a slight molecular change and increase of magnetism oc- 

 curred ; and in fifteen seconds more a sudden and more powerful 

 change of the same kind took place, producing a deflection of the 

 needles of 6° ; the needles then returned to their original position. 



