constantly maintained in contact with it, and the circuit is only completed when a point of the copper slip dips in the mercury also; but the circuit is broken the moment that point rises above it. Thus, by the rotation of the armature, the circuit is alternately broken and renewed; and as it is only at these moments that electric action is manifested, a brilliant spark takes place every time the copper point touches the surface of the mercury. Platina wire is ignited, shocks smart enough to be disagreeable are given, and water is decomposed with astonishing rapidity, by the same means, which proves beyond a doubt the identity of the magnetic and electric agencies, and places Mr. Faraday, whose experiments established the principle, in the first rank of experimental philosophers.'-pp. 339, 340.

The following speculations are somewhat insecure, but they are proposed as conjectures rather than assertions, and are well worth

notice :

From the experiments of Mr. Faraday, and also from theory, it is possible that the rotation of the earth may produce electric currents in its own mass. In that case, they would flow superficially in the meridians, and if collectors could be applied at the equator and poles, as in the revolving plate, negative electricity would be collected at the equator, and positive at the poles; but without something equivalent to conductors to complete the circuit, these currents could not exist.

'Since the motion, not only of metals but even of fluids, when under the influence of powerful magnets, evolves electricity, it is probable that the gulf stream may exert a sensible influence upon the forms of the lines of magnetic variation, in consequence of electric currents moving across it, by the electro-magnetic induction of the earth. Even a ship passing over the surface of the water, in northern or southern latitudes, ought to have electric currents running directly across the line of her motion. Mr. Faraday observes, that such is the facility with which electricity is evolved by the earth's magnetism, that scarcely any piece of metal can be moved in contact with others without a development of it, and that consequently, among the arrangements of steam engines and metallic machinery, curious electro-magnetic combinations probably exist, which have never yet been noticed.

What magnetic properties the sun and planets may have it is impossible to conjecture, although their rotation might lead us to infer that they are similar to the earth in this respect. According to the observations of MM. Biot and Gay-Lussac, during their aerostatic expedition, the magnetic action is not confined to the surface of the earth, but extends into space. A decrease in its intensity was perceptible; and as it most likely follows the ratio of the inverse square of the distance, it must extend indefinitely. It is probable that the moon has become highly magnetic by induction, in consequence of her proximity to the earth, and because her greatest diameter always points towards it. Should the magnetic, like the gravitating force,

extend through space, the induction of the sun, moon, and planets must occasion perpetual variations in the intensity of terrestrial magnetism, by the continual changes in their relative positions.

In the brief sketch that has been given of the five kinds of electricity, those points of resemblance have been pointed out which are characteristic of one individual power; but as many anomalies have been lately removed, and the identity of the different kinds placed beyond a doubt by Mr. Faraday, it may be satisfactory to take a summary view of the various coincidences in their modes of action on which their identity has been so ably and completely established by that great electrician.'-pp. 352-354.

We shall not here pursue this subject, as the examination of it at suitable length would lead us too far. We add some examples of the information contained in this work :—

'M. Melloni, observing that the maximum point of heat is transferred farther and farther towards the red end of the spectrum, according as the substance of the prism is more and more permeable to heat, inferred that a prism of rock-salt, which possesses a greater power of transmitting the calorific rays than any other known body, ought to throw the point of greatest heat to a considerable distance beyond the visible part of the spectrum-an anticipation which experiment fully confirmed, by placing it as much beyond the dark limit of the red rays as the red part is distant from the bluish-green band of the spectrum.'-p. 237.

The establishment of the identity of charcoal and diamond led sanguine persons to anticipate the time when our home-manufactures should rival the produce of Golconda. In such speculations it is but reasonable to take into account the reflection with which Mrs. S. closes the following passage:

'It had been observed that, when metallic solutions are subjected to galvanic action, a deposition of metal, generally in the form of minute crystals, takes place on the negative wire: by extending this principle, and employing a very feeble voltaic action, M. Becquerel has succeeded in forming crystals of a great proportion of the mineral substances precisely similar to those produced by nature. The electric state of metallic veins makes it possible that many natural crystals may have taken their form from the action of electricity bringing their ultimate particles, when in solution, within the narrow sphere of molecular attraction already mentioned as the great agent in the formation of solids. Both light and motion favour crystallization. Crystals which form in different liquids are generally more abundant on the side of the jar exposed to the light; and it is a well-known fact that still water, cooled below thirty-two degrees, starts into crystals of ice the instant it is agitated. Light and motion are intimately connected with electricity, which may, therefore, have some influence on the laws of aggregation; this is the more likely, as a feeble action is alone necessary, provided it be continued for a sufficient time. Crys

1.

tals

tals formed rapidly are generally imperfect and soft, and M. Becquerel found that even years of constant voltaic action were necessary for the crystallization of some of the hard substances. If this law be general, how many ages may be required for the formation of a diamond!'-pp. 307, 308.

The following is the history of the successive approximations to the place of the magnetic pole :

In the year 1819, Sir Edward Parry, in his voyage to discover the north-west passage round America, sailed near the magnetic pole; and in 1824, Captain Lyon, on an expedition for the same purpose, found that the magnetic pole was then situated in 63° 26′ ‍51′′ north latitude, and in 80° 51' 25" west longitude. It appears, from later researches, that the law of terrestrial magnetism is of considerable complexity, and the existence of more than one magnetic pole in either hemisphere has been rendered highly probable; that there is one in Siberia seems to be decided by the recent observations of M. Hansteen,-it is in longitude 102° east of Greenwich, and a little to the north of the 60th degree of latitude: so that, by these data, the two magnetic poles in the northern hemisphere are about 180° distant from each other: but Captain Ross, who is just returned from a voyage in the polar seas, has ascertained that the American magnetic pole is in 70° 14' north latitude, and 96° 40' west longitude. The magnetic equator does not exactly coincide with the terrestrial equator; it appears to be an irregular curve, inclined to the earth's equator at an angle of about 12°, and crossing it in at least three points in longitude 113° 14' west, and 66° 46' east of the meridian of Greenwich, and again somewhere between 156° 30′ of west longitude, and 116° east.'-pp. 310, 311.

We may add that the place thus determined by Captain Ross agrees with that collected from considerations, which we conceive to be more trustworthy than observations made at one place, with so imperfect an instrument as a dipping needle is for such purposes. In Mr. Barlow's Memoir On the present situation of the Magnetic Lines of Equal Variation,' just published in the Philosophical Transactions, he says, 'The pole itself'—(as deter mined by Captain Ross and his nephew) is precisely that point on my globe and chart, in which, by supposing all the lines to meet, the separate curves would best preserve their unity of character, both separately and as a system.'

Our readers cannot have accompanied us so far without repeatedly feeling some admiration rising in their minds, that the work of which we have thus to speak is that of a woman. There are various prevalent opinions concerning the grace and fitness of the usual female attempts at proficiency in learning and science; and it would probably puzzle our most subtle analysts of common sense or common prejudice to trace the thread of rationality or irrationality

which runs through such popular judgments. But there is this remarkable circumstance in the case, that where we find a real and thorough acquaintance with these branches of human know ledge, acquired with comparative ease, and possessed with unob. trusive simplicity, all our prejudices against such female acquirements vanish. Indeed, there can hardly fail, in such cases, to be something peculiar in the kind, as well as degree, of the intellectual character. Notwithstanding all the dreams of theorists, there is a sex in minds. One of the characteristics of the female intellect is a clearness of perception, as far as it goes with them, action is the result of feeling; thought, of seeing; their practica emotions do not wait for instruction from speculation; their reasoning is undisturbed by the prospect of its practical consequences. If they theorize, they do so

In regions mild, of calm and serene air,

Above the smoke and stir of this dim spot
Which men call earth.'

Their course of action is not perturbed by the powers of philosophic thought, even when the latter are strongest. The heart goes on with its own concerns, asking no counsel of the head; and, in return, the working of the head (if it does work) is not impeded by its having to solve questions of casuistry for the heart. In men, on the other hand, practical instincts and theoretical views are perpetually disturbing and perplexing each other. Action must be conformable to rule; theory must be capable of application to action. The heart and the head are in perpetual negotiation, trying in vain to bring about a treaty of alliance, offensive and defensive. The end of this is, as in many similar cases, inextricable confusion- -an endless seesaw of demand and evasion. In the course of this business, the man is mystified; he is involved in a cloud of words, and cannot see beyond it.

He does not know whether his opinions are founded on feeling or on reasoning, on words or on things. He learns to talk of matters of speculation without clear notions; to combine one phrase with another at a venture; to deal in generalities; to guess at relations and bearings; to try to steer himself by antitheses and assumed maxims. Women never do this: what they understand, they understand clearly; what they see at all, they see in sunshine. It may be, that in many or in most cases, this brightness belongs to a narrow Goshen; that the heart is stronger than the head; that the powers of thought are less developed than the instincts of action. It certainly is to be hoped that it is so. But, from the peculiar mental character to which we have referred, it follows, that when women are philosophers, they are likely to be lucid ones; that when they extend the range of their specula

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tive

tive views, there will be a peculiar illumination thrown over the prospect. If they attain to the merit of being profound, they will add to this the great excellence of being also clear.

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We conceive that this might be shown to be the case in such women of philosophical talent as have written in our own time. But we must observe, that none of these appear to have had possession of the most profound and abstruse province of human knowledge, mathematics, except the lady now under review. Indeed, the instances of eminent female mathematicians who have appeared in the history of the world are very rare. There are only two others who occur to us as worthy of entirely honourable notice-Hypatia and Agnesi; and both these were very extraordinary persons. It is, indeed, a remarkable circumstance, that the Principia' of Newton were in the last century translated and commented on by a French lady; as the great French work on the same subject, in our own time, the Mécanique Céleste' of Laplace, has been by a lady of this country. But Madame de Chastelet's whole character and conduct have not attracted to her the interest which belongs to the other two. The story of Hypatia is unhappily as melancholy as it is well known. She was the daughter of Theon, the celebrated Platonist and mathematician of Alexandria, and lived at the time when the struggle between Christianity and Paganism was at its height in that city. Hypatia was educated in the doctrines of the heathen philosophy, and in the more abstruse sciences; and made a progress of which contemporary historians speak with admiration and enthusiasm. Synesius, bishop of Ptolemais, sends most fervent salutations to her, the philosopher, and that happy society which enjoys the blessings of her divine voice.' She succeeded her father in the government of the Platonic school, where she had a crowded and delighted audience. She was admired and consulted by Orestes, the governor of the city, and this distinction unhappily led to her destruction. In a popular tumult she was attacked, on a rumour that she was the only obstacle to the reconciliation of the governor and of Cyril the archbishop. On a fatal day,' says Gibbon, in the holy season of Lent, Hypatia was torn from her chariot, stripped naked, dragged to the church, and inhumanly butchered by the hands of Peter the reader and a troop of savage and merciless fanatics: her flesh was scraped from her bones with oyster-shells, and her quivering limbs were delivered to the flames.'

From this strange and revolting story, we turn to the other name which we have mentioned, Madame Agnesi, who flourished during the last century at Bologna, where her father was professor; and when the infirmity of his health interfered with his discharge

of