(TWENTY-FIFTH MEMOIR.)

EXPERIMENTAL AND THEORETICAL.

465

Seventh Experiment.

Hollow Iron Bar, cold (End A,and unagitated, End B,

End B,

deflection 27°)

Mean, 27-25'

deflection 33

>-Mean, 33-5°

deflection 34

j

78. By comparing the results obtained by the simple process of agitation with thosewhich the iron gave by cooling from a high temperature, the difference will beobserved to be so inconsiderable as to show that the magnetic action due to the latteris not much superior to that due to the former process ; nor indeed at all more so thanmay be fairly accounted for by the molecular movements within the ferruginous massesemployed (72).

79. In pursuing the views I had already taken respecting the complete expulsionof the magnetic matter by means of heat (66-71), it appeared likely that a bar ofiron might be converted into a series of distinct magnets by heating it to a high tem-perature in several different parts, and permitting the intervening parts to remaincomparatively cool, or below that temparature at which magnetic action was completein the previously conducted experiments (55-62); and being desirous of embodyingin this Memoir all the facts I could collect on this topic, I called on Mr. Fothergill,who had assisted me in all the previous experiments, about one o’clock this after-noon, to request his assistance again in procuring me a few more heats of the iron.This request was readily assented to, and the following experiments were made, atthe Atlas Works, after four o’clock this evening.

Eighth Experiment.

80. The solid iron bar, No. 1, two feet long, was heated to a high degree of rednessat one of its ends to nearly the middle of the bar, whilst the other part was kept com-paratively cool, and afterwards still further cooled by immersion in the slake-trough.The bar thus treated was then placed in the line of the dip, as in former experiments,with its heated end uppermost, having the compass needle at the distance of six incheson the eastern side.

The hot end showed no magnetic action whatever. I now requested the smith whoassisted me to raise the bar till nearly the whole of the heated part was above thecompass. In this position the north end of the needle was drawn towards the barabout 25°, indicating the presence of a pole of the opposite kind.

The character and situation of this pole being ascertained, the bar was again gradu-ally raised till its lower extremity was level with the compass. The deflection of theneedle at first declined, and gradually returned to the meridian as the centre, or

3 L