as nature-poker *, or nature-peeper, for these naturæ curiosi; but these were indignantly rejected.

The inconveniences of this division of the soil of science into infinitely small allotments have been often felt and complained of. It was one object, we believe, of the British Association, to remedy these inconveniences by bringing together the cultivators of different departments. To remove the evil in another way is one object of Mrs. Somerville's book. If we apprehend her purpose rightly, this is to be done by showing how detached branches have, in the history of science, united by the discovery of general principles.

'In some cases identity has been proved where there appeared to be nothing in common, as in the electric and magnetic influences; in others, as that of light and heat, such analogies have been pointed out as to justify the expectation that they will ultimately be referred to the same agent; and in all there exists such a bond of union, that proficiency cannot be attained in any one without a knowledge of others.'-Preface.

We may add, that in the same way in which a kindred language proves the common stock and relationship of nations, the connexion of all the sciences which are treated of in the work now before us is indicated by the community of that mathematical language which they all employ. Our space does not allow us to dwell on the illustration of this point, but we may select a passage or two. We cannot even refer to the curious sections on the properties of light; on the fringes of shadows, the colours of thin plates, the results of polarization, and of the analysis of polarized light after passing through crystals; on the evidence and proofs of the undulatory theory; which last great question our author, rightly, as we conceive, judges to be now nearly'settled in favour of the undulationists. But we may quote what she says on one of the analogies which we have already noticed :

It has been observed that heat, like light and sound, probably consists in the undulations of an elastic medium. All the principal phenomena of heat may actually be illustrated by a comparison with those of sound. The excitation of heat and sound are not only similar, but often identical, as in friction and percussion; they are both communicated by contact and radiation; and Dr. Young observes, that the effect of radiant heat in raising the temperature of a body upon which it falls resembles the sympathetic agitation of a string, when the sound of another string, which is in unison with it, is transmitted

* When the German association met at Berlin, a caricature was circulated there, representing the 'collective wisdom' employed in the discussion of their mid-day meal with extraordinary zeal of mastication, and dexterity in the use of the requisite implements, to which was affixed the legend- Wie die natur-forscher natur-forschen,' which we venture to translate the poking of the nature-pokers.'

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to it through the air. Light, heat, sound, and the waves of fluids, are all subject to the same laws of reflection, and, indeed, their un-dulatory theories are perfectly similar. If, therefore, we may judge from analogy, the undulations of some of the heat-producing rays must be less frequent than those of the extreme red of the solar spectrum; but if the analogy were perfect, the interference of two hot rays ought to produce cold, since darkness results from the interference of two undulations of light-silence ensues from the interference of two undulations of sound-and still water, or no tide, is the consequence of the interference of two tides. The propagation of sound, however, requires a much denser medium than that either of light or heat; its intensity diminishes as the rarity of the air increases; so that at a very small height above the surface of the earth the noise of the tempest ceases, and the thunder is heard no more in those boundless regions where the heavenly bodies accomplish their periods in eternal and sublime silence.'-pp. 250, 251.

We refer to the following on account of the novelty of the subject :

After Mr. Faraday had proved the identity of the magnetic and electric fluids by producing the spark, heating metallic wires, and accomplishing chemical decomposition, it was easy to increase these effects by more powerful magnets and other arrangements. The following apparatus is now in use, which is in effect a battery, where the agent is the magnetic instead of the voltaic fluid, or, in other words, electricity.

A very powerful horse-shoe magnet, formed of twelve steel plates in close approximation, is placed in a horizontal position. An armature consisting of a bar of the purest soft iron has each of its ends bent at right angles, so that the faces of those ends may be brought directly opposite and close to the poles of the magnet when required. Two series of copper wires-covered with silk, in order to insulate them are wound round the bar of soft iron as compound helices. The extremities of these wires, having the same direction, are in metallic connexion with a circular disc, which dips into a cup of mercury, while the ends of the wires in the opposite direction are soldered to a projecting screw-piece, which carries a slip of copper with two opposite points. The steel magnet is stationary; but when the armature, together with its appendages, is made to rotate horizontally, the edge of the disc always remains immersed in the mercury, while the points of the copper slip alternately dip in it and rise above it. By the ordinary laws of induction, the armature becomes a temporary magnet while its bent ends are opposite the poles of the steel magnet, and ceases to be magnetic when they are at right angles to them. It imparts its temporary magnetism to the helices which concentrate it; and while one set conveys a current to the disc, the other set conducts the opposite current to the copper slip. But as the edge of the revolving disc is always immersed in the mercury, one set of wires is

constantly

constantly maintained in contact with it, and the circuit is only com, pleted 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 aërostatic 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 elec tricity, 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-manu, factures 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

tals

tals formed rapidly are generally imperfect and soft, and M. Becque rel 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.

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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