.! . Changes, in Iron §c\ at different Temperatures. 175 



Cold water being now very freely applied to the black hot bar, a 

 similar deflection of 1|° occurred; part of this last deflection 

 was probably due to the more rapid cooling. 



With a bar of cast iron 30 inches ( = 76*2 centims.) long and 

 | of an inch ( = 19 millims.) in diameter, and the same wire coils 

 and battery, the effects obtained were similar, but much more 

 feeble than with the bar of steel. At a feeble elevation of tem- 

 perature, below that at which a similar effect took place in the 

 steel bar, a feeble sudden molecular movement and decrease of 

 magnetism took place. At a red heat a second similar change 

 occurred. Soon after this the gas was stopped and the bar 

 allowed to cool ; in about twenty seconds a molecular change 

 commenced, feeble at first and then suddenly stronger, producing 

 a deflection of 6° and then ceasing, as with the steel bar. 



Various other small irregularities in these molecular changes 

 in wrought iron, cast iron, and steel were observed, but are not 

 here recorded ; and each different bar gave somewhat different 

 results. If the processes of heating and cooling were more rapid, 

 all the changes would be more powerful. 



The results I have obtained with bars of wrought iron, steel, 

 and cast iron by the foregoing plan agree in the main with those 

 of M. Mauritius*, obtained by quite a different method. He 

 found that at a bright red heat none of the bars were mag- 

 netic ; on cooling a red-hot steel bar the magnetism increased at 

 first very rapidly, then for a certain time slowly, and then again 

 followed a second period of rapid increase; cast iron behaved 

 similarly but in a less degree ; and with wrought iron the second 

 increase does not exist. He considers the magnetism of iron is 

 developed suddenly at a particular temperature of about 1000°. 



With a bar of cast nickel about 18 inches ( = 45*7 centims.) 

 long and J an inch ( = 12*7 millims.) thick the following effects 

 were obtained : — During heating, a slow deflection of 1^° was 

 obtained at a particular temperature much below a red heat ; and 

 duriug cooling, a deflection of 1J° in an opposite direction oc- 

 curred, apparently at the same temperature ; no other deflections 

 were obtained by heating the bar gradually to redness and then 

 cooling. With another bar of that metal, 2 feet ( = 61 centims.) 

 long and J of an inch (=19 millims.) in diameter f, a thick-wire 

 coil6inches ( = 15*2centims.) long and 2^ inches ( = 5*7 centims.) 

 in diameter, containing 8 layers or 536 turns of " No. 17 " (=1*5 

 raillim. thick) copper w T ire, and a thin-wire coil 6 inches long and 

 and 2 inches in diameter, containing 14 layers or 1960 turns of 

 "No. 27" ( = 0*25 milliin. thick) copper wire, on applying the 



* Phil. Mag. 1864, vol. xxvii. p. 399. 



t Obtained by the kindness of H. Wiggin, Esq., of the firm of Messrs, 

 Evans and Askin, nickel-refiners, Birmingham. 



