(TWENTY-FOURTH MEMOIR.)

EXPERIMENTAL AND THEORETICAL.

449

them, it will be necessary to ascertain in what manner the magnetic poles are affectedby placing the point of heat between them, before the phenomena can be applied to theexplication of terrestrial magnetic mutations. The following experiments were madefor this purpose:—

Twenty-sixth Experiment.

32. The eight-inch magnet (2) was retouched and placed horizontally at rightangles to the magnetic meridian, having a needle arranged at each pole, as in Fig. 10,directly opposite to the centres of magnetic force. The lamp was placed directly underthe centre of the magnet. In one minute both needles began to move, and in fiveminutes each needle had attained a deflection of 5° or thereabouts. The deflectionswere in the directions represented by the dotted needles, showing that both poles ofthe magnet had moved outwards , or, as in the previous experiments, from the point ofheat.*

33. This important result in connection with those results obtained by Experiments23, 24, and 25, appear to develop a certain determinate action which caloric exerciseson the poles of the magnet, viz.—That the magnetic poles move from the point ofheat ; or in general, that the magnetic poles move in the direction of the calorific current.Should this law become established by future experiments, and that it can be provedexperimentally that a current of caloric will move the magnetic poles laterally as wellas in the direction of their axes, there would be little difficulty in accounting for therevolutions of the terrestrial magnetic poles in their respective latitudes ; and I haveno doubt, from the results of some experiments that I have made with flat pieces ofsteel, that the magnetic poles of the earth are susceptible of a lateral translation bythe direct action of solar heat alone ; and that by means of a magnetized steel globeand a spirit lamp, I can readily suppose that the revolutions of the terrestrial magneticpoles might be very beautifully imitated. But I have not, at present, any more sparetime to devote to this interesting subject; I must, therefore, content myself, till somemore favourable opportunity presents itself, with having called the attention of philo-sophers to this novel mode of investigation, being perfectly aware that there yet remainsa rich harvest for those who may venture on the pursuit. In conclusion, I would begpermission to state that the expansions and contractions of the magnetic axis, as shownby Experiments 23, 24, 25 and 26, appear to me to afford sufficient data for supposingthat the terrestrial magnetic axis suffers similar mutations by the direct action of thesun, and that the phenomena of diurnal variation, and change of intensity on the needle,are probably traceable to these secondary causes.

* These results, which are so very different to any hitherto made known, cannot be accounted for upon any supposed motionsof the neutral plane of the magnet, in the manner which has been attempted to explain some of the interesting phenomenadiscovered by MM. Coulomb and Kupffer.

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