representation of the path of the comet among the stars, according to each of these three mathematicians, its places being marked from Aug. 7, 1835, to Feb. 7, 1836. The positions, according to the different computations, though not very far asunder, are sufficiently distinct to make the separation, at a certain period, very wide. M. Pontécoulant, M. Damoiseau, and Mr. Lubbock, start their comets close together in August; but by the 4th of October, Pontécoulant is a whole length behind Damoiseau, (except these fiery steeds' have bodies and tails of portentous prolixity,) and Lubbock decidedly shoots a-head of both. It will be extremely interesting, when the period arrives, to observe which of the three lines Comet himself will select. We recommend this subject to those of our friends who have taken an interest in our recent philosophical disquisitions concerning the Turf, and especially if their adverse stars' prohibit a visit to Newmarket: for the stars, in this case, offer them a very sufficient compensation; and our amateurs, by backing one of the three calculated paths of this courser of celestial race,' as the true one, to be decided' by the comet himself when he makes his appearance, may have the luxury of higher play than has yet been known.

But we must return to Mrs. Somerville's chapter on Comets, and quote the account of another of these curious bodies. After speaking of Encke's comet, which has a period of 1207 days, she

says

'The other comet belonging to our system, which returns to its perihelion after a period of 63 years, has been accelerated in its motion by a whole day during its last revolution, which puts the existence of ether beyond a doubt, and forms a strong presumption in corroboration of the undulating theory of light. The comet in question was discovered by M. Biela at Johannisberg on the 27th of February, 1826, and ten days afterwards it was seen by M. Gambart at Marseilles, who computed its parabolic elements, and found that they agreed with those of the comets which had appeared in the years 1789 and 1795, whence he concluded them to be the same body moving in an ellipse, and accomplishing its revolution in 2460 days. The perturbations of this comet were computed by M. Damoiseau, who predicted that it would cross the plane of the ecliptic on the 29th of October, 1832, a little before midnight, at a point nearly 18484 miles within the earth's orbit; and as M. Olbers, of Bremen, in 1805, had determined the radius of the comet's head to be about 21136 miles, it was evident that its nebulosity would envelop a portion of the earth's orbit-a circumstance which caused great alarm in France, and not altogether without reason, for if any disturbing cause had delayed the arrival of the comet for one month, the earth must have through passed its head. M. Arago dispelled their fears by the excellent treatise on comets which appeared in the Annuaire of 1832, where

where he proves that, as the earth would never be nearer the comet than 24800000 British leagues, there could be no danger of collision.' -pp. 369-70.

We may observe that the alarm of which Mrs. Somerville here speaks, affords an example of the confusion of ideas, which popular views of scientific matters often involve; and thus shows us how valuable a boon it is to the mass of readers, when persons of real science, like Mrs. Somerville, condescend to write for the wider public, as in this work she does. The apprehensions with regard to Biela's (or, as it ought rather to be called, Gambart's) comet, which were entertained by our worthy neighbours, tout le monde of Paris, were of a kind somewhat peculiar. The expected arrival of this visiter, with his fiery train, produced a commotion scarcely inferior to that which was excited among the good people of Strasburg by the stranger in the red-plush inexpressibles. That his head or his tail would do us irreparable harm-that he would burn us with his nucleus-or drown or poison us with his atmosphere were slight terrors compared with those excited by the combination of terms perturbations' and 'orbite de la terre.' It appeared that the comet would cross the earth's orbit; what mischief might not come of this? It was true that the earth would not be near the crossing at that time; but then, might not the orbit itself be seriously injured? Instead of an imaginary line in the trackless ocean of space, the fears of our friends appear to have represented to them the earth's orbit as a sort of railroad, which might be so damaged by what Mr. Campbell calls the bickering wheels and adamantine car' of the fiery giant,' that the earth must stick or run off, the next time the revolving seasons brought her to the fatal place. In M. Arago's agreeable and instructive article in the Annuaire du Bureau des Longitudes,' written in order to calm the panic arising from these horrible imaginings,' he

says,

'Shall I be so fortunate as to do this? I hope so; yet without being very confident. Have I not seen persons who, while they acknowledged that the earth would not receive, in 1832, any direct blow from the comet, still believed that this body could not go through our orbit without altering its form; as if this orbit was a material thing; as if the parabolic path which a bomb is just going to describe, could be affected by passing through the space which other bombs had traversed before !!'

But we must not dwell too long on one part of Mrs. Somerville's work; we must recollect that her professed object is to illustrate The Connexion of the Physical Sciences.' This is a noble object; and to succeed in it would be to render a most important service to science. The tendency of the sciences has

long

long been an increasing proclivity to separation and dismemberment. Formerly, the learned' embraced in their wide grasp all the branches of the tree of knowledge; the Scaligers and Vossiuses of former days were mathematicians as well as philologers, physical as well as antiquarian speculators. But these days are past; the students of books and of things are estranged from each other in habit and feeling. If a moralist, like Hobbes, ventures into the domain of mathematics, or a poet, like Goethe, wanders into the fields of experimental science, he is received with contradiction and contempt; and, in truth, he generally makes his incursions with small advantage, for the separation of sympathies and intellectual habits has ended in a destruction, on each side, of that mental discipline which leads to success in the other province. But the disintegration goes on, like that of a great empire falling to pieces; physical science itself is endlessly subdivided, and the subdivisions insulated. We adopt the maximone science only can one genius fit.' The mathematician turns away from the chemist; the chemist from the naturalist; the mathematician, left to himself, divides himself into a pure mathematician and a mixed mathematician, who soon part company; the chemist is perhaps a chemist of electro-chemistry; if so, he leaves common chemical analysis to others; between the mathematician and the chemist is to be interpolated a 'physicien' (we have no English name for him), who studies heat, moisture, and the like. And thus science, even mere physical science, loses all traces of unity. A curious illustration of this result may be observed in the want of any name by which we can designate the students of the knowledge of the material world collectively. We are informed that this difficulty was felt very oppressively by the members of the British Association for the Advancement of Science, at their meetings at York, Oxford, and Cambridge, in the last three summers. There was no general term by which these gentlemen could describe themselves with reference to their pursuits. Philosophers was felt to be too wide and too lofty a term, and was very properly forbidden them by Mr. Coleridge, both in his capacity of philologer and metaphysician; savans was rather assuming, besides being French instead of English; some ingenious gentleman proposed that, by analogy with artist, they might form scientist, and added that there could be no scruple in making free with this termination when we have such words as sciolist, economist, and atheist-but this was not generally palatable; others attempted to translate the term by which the members of similar associations in Germany have described themselves, but it was not found easy to discover an English equivalent for natur-forscher. The process of examination which it implies might suggest such undignified compounds

as

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.'

to

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 undulatory 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.

6 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