Lapas attēli

entered the vessel on opposite sides, and could be made to communicate at will, with the opposite poles of a battery. Now the wire p, being positive, and n negative, the extremity a of the suspended needle would be negative, and the extremity c positive, by induction. The conjoined effort of the forces thus brought to bear on the needle, acting on its opposite extremities, in opposite directions, would solicit it to move on its axis, the extremity a in the direction n' figure 8, and the extremity c in the direction p', the line of rest would be as expressed by the dots in the figure, and slow oscillations should take place on either side of that line, if the density, or other properties of the medium permitted.

9. The experiment was thus tried, and to prevent any derangement from hygrometric twist of the silk, the needle was hung on a glass thread, of sufficient length to reach above the surface of the water, and there attached to the silk; on passing the current of forty-five pairs of four inch plates, the needle immediately moved, and after two or three oscillations, took its position of rest; on being moved to the opposite side of the polar wire, an opposite motion ensued, until the same position was gained. During this movement, gas was freely liberated from the extremities of the polar wires, and also from both ends of the needle, which hindered considerably that freedom of motion, which I had hoped for in observing the oscillations, The experiment was also varied, by terminating the polar wires with plates of platina, with a view of increasing the effect; the needle was also suspended in pyroligneous ether, and the attractive power of the same battery, newly charged, was very marked; it was not so observable in alcohol, and still less in muriatic acid; in ammonia, though only one end of the needle appeared to evolve gas, it was not so obedient to the attractive force. These cir. cumstances indicate that the phenomena of motion, as here exhibited, have not their origin in any magnetic action produced either by the disturbance of the earth or the passage of the voltaic currents. Magnetic action to be complete, requires that the bodies, along which currents are passing, should be possessed of high conducting power, hence a thermal current whose tension is almost extinct, is still capable of producing a powerful effect on a suspended needle. A current capable of producing a given deviation when moving along metallic wires would meet with resistance in passing through water, and alcohol, or ether would forbid its passage. It is moreover impossible to produce any visible effect on the platina wire of this arrangement by the action of a solitary pair, even possessing extensive surface, though the same pair if cut into lesser plates, and arranged for the production of a current of greater tension, immediately causes the movement here described. Dr. Faraday has stated, in his recent researches on this point, that there is not any proof that the poles of a battery do exercise any power of attraction or repulsion, (Bache's, Turner's Chem. page 102, idem 108,) but that opinion would appear to be inconsistent with the fact—there must be an

accumulation of tension on an electrode, if the medium

which separates it from its fellow, is not so good a 9.

conductor as the liquid filling the cells of the battery; and experiment warrants this conclusion.

10. The principles here laid down, also indicate the construction of a GALVANOMETER, figure 9, which I have recently fitted up. It is intended to exhibit by the torsion of a fine fibre, the force of attraction between the polar wires, and the ends of the suspended needle. The only obstacle I have as yet observed to the accu

[ocr errors]

racy of the result furnished by it, is due to the development of gas on the polar wires, and on the needle.

11. The doctrine which I wish to establish from this experiment, is, that though the polar wires are plunged in a conducting medium, and the current is actually passing, yet they still act as centres of attraction. The motions of mercury and other fluids are only exemplifications of this doctrine.

12. When a spheroidal mass of conducting matter, is brought in presence of a point of attraction, situated at a distance from its surface, the particles on that surface will be differently affected, as their situation in regard to the attracting point varies. Thus on touching the mercurial globule, named in the first part of this paper, with a negative wire, and introducing into

the water a positive platina pole, the globule, which

before was spherical, becomes elliptical, as represented 10.

in figure 10, two tides are formed upon it, as at a and b, Pone directly opposite the positive wire p, and the other

180 degrees from it, meanwhile there is an ebb in those regions which are situate a quadrant from the point

of attraction. If the positive wire is made to revolve round the globule, both tides move, always keeping the same relative position to the point of attraction, that they had at first. It only requires the force of the battery to be appropriately moderated, to exhibit these phenomena with the utmost rigidness. And, as these motions exhibit very nearly, on a small scale, that effect which takes place on an immense scale, by the joint action of the Sun and Moon, in producing the tides of the ocean, I have given them the name of Tidal motions of Conductors, free to move.

13. Now the mechanism which produces the change of figures, from a sphere to an ellipsoid is sufficiently obvious. We have two forces under

consideration. 1st. The cohesion or gravitation of the mercurial particles upon each other;-and, 2nd, the disturbing force of the polar wire, as a centre of attraction. As that disturbing force decreases in a certain ratio, as the distances increase, the mercurial particles on the side

A, figure 11, nearest to the polar wire, are more attracted B by it than those in the centre C of the globule, and those

in the centre C, are more attracted than those at F. The particles, therefore, at A, rise towards the wire by its direct action, those at F, being less solicited towards the centre of the globule than those at E and B, the former recede from that centre, while the latter seek it.

14. It has been observed, that a true theoretical tide differs in no respect from a wave. Suppose a spring tide actually formed on a fluid sphere, and the sun and moon then annihilated, the elevation must sink, pressing the under waters aside, and causing them to rise, where they were depressed. The motion will not stop, when the surface comes to a level, for the waters arrive at that position, with a motion continually accelerated. They, therefore, pass that position, as a pendulum passes the perpendicular, and will rise as far on the other side, forming a high water where it was low water, and low water where it was high water. And this would go on forever, oscillating in an assignable time, if it were not for the viscidity of the water. Now this theoretical case may be easily shown, for on approaching the positive wire towards the globule of mercury, a particular position will be gained, at which contact will take place, between the protuberant tide on the mercury and the wire. Io that moment the cause of attraction is annihilated, the whole current of electricity now passes along perfect conduc




tors, hence fulfilling the supposed case of an actual annihilation of the sun and moon, at the time of a spring tide. And the same reasoning that held in one case, equally applies in the other; the mercurial tide falls with an accelerated motion, and the line which before was the conjugate axis of the ellipse, now becomes the transverse; a tide being produced at right angles to the former one. But here the strict comparison ends, for as the mercury ebbs from its protuberant position, the metallic connexion breaks, and the wire is again put in action as a point of attraction,-the motion of the ebbing tide is checked, -it flows once more, -once more the metallic contact is complete, and when the tide falls,-it is only to flow again, as long as the battery current passes. Tides take place at right angles to each other, in a series too rapid to be counted, and the whole surface of the mercury is worked into those various and beautiful undulations which have been before refer. red to..

15. In endeavouring to ascertain the true cause of these phenomena, the French philosphers were, I believe, the first to observe these motions in the water, or other liquid of communication, as if a gentle wind played over its surface, bearing light bodies in its vortices. The explanation of these appearances, I here add, because no one as yet has given it, and it affords an illustration of certain propositions delivered by Sir I. Newton, in his principia, concerning the doctrine of pulses in elastic fluids.

16. We have hitherto been considering a globule of mercury, as a substance mathematically fluid. Such, however, in effect it is not, the water in contact with it possesses those properties in a much more eminent degree, so that in comparison with it, the mercury may be regarded, as a solid resisting obstacle.. Now about a year ago, I showed that when a voltaic current passes through a system such as this of mercury and water, the capillary pressure on the bounding surface is changed; but, if the attraction of the wire which is introduced into the water, and which is the ultimate cause of this dynamical derangement decreases in a duplicate ratio, it follows that this disturbance of pressure, obtains only to a limited extent on the surface of the mercury; or in other words, the excess of pressure produced by a voltaic current, is not spent equally on all parts of the mercurial surface, but those which are adjacent to the positive polar wire, are more affected than those at a distance. Newton has shown (Pr. v. 2, B. 2, pr. 41) that if the particles of a fluid do not lie in a right line, a pressure propagated through that fluid, will not be in rectilineal direction, but the particles

that are obliquely posited, have a tendency to be urged out

of their position. So the particles a a a a, figure 12, pressing
on the particles d b, which stand obliquely to them, by rea-
son of ihe shape of the mass of mercury g, have a tendency
to be urged from their places towards e and c respectively,
and the motion thus produced in a fluid, diverges from a
rectilinear progress into the unmoved spaces,

and such
a pressure taking effect on a liquid free to move, continu.

ally return the moving particles, to their first position, after making them describe an elliptical orbit.

17. It has been remarked, that the basis on which this explanation essentially rests, is that a wire, from which an electric current passes, acts still as a point of attraction; an effect which involves the conducting and other electric properties of the system, on which the experiment is traced. Hence we gain an insight into the cause of the paralysis of these motions, by the addition of certain substances,—the spiral motions going on the surface of

[ocr errors]
[ocr errors]
[ocr errors]

the water, have these explanations complicated with another consideration, -the figure of the mercurial mass.

Observations upon the facts recently presented by Professor Olmsted, in relation to Meteors seen on the 13th of November, 1854. By A. D. BACHE, Prof. Nat. Philos. and Chem. Univ. Penn. Before proceeding to examine the new facts recently put forth by my friend, Prof. Olmsted, in regard to meteors seen on the i2th and 13th of November, 1834, it will be well to state what is the difference of opinion between us.

Prof. Olmsted I understand to assert, that there was a recurrence of the meteoric display of November, 1833, in 1834, thus verifying a prediction made by him as a consequence of his peculiar theory. With that theory, further than as it is borne upon by facts in regard to the prediction founded upon it, I have not at present any concern. Independently of theory, it would be a very curious fact, if it were made out, that meteoric displays of an nousual kind occurred annually on the same night; and I was induced to observe on the night of the 12th-13th of November, 1834, with reference to facts rather than theory. Prof. Olmsted states his conclusions from ob. servations made at New Haven, in these words: “On the morning of the 13th of November, 1834, there was a slight recurrence of the meteoric shower wbich presented so remarkable a spectacle on the corresponding morning of 1833.5*

My views, as resulting, first, from observations made at Philadelphia on the morning of the 13th, are, that "there occurred on the 13th of Novem. ber, 1834, no remarkable display of meteors of the kind witnessed in 1833." To sustain this, after recording the meteors seen by me on the 13th of No. vember, 1834, I undertook to show, 1. That the meteors which I saw were Deither in degree nor in their peculiarities like a portion of the meteoric phenomenon of November, 1833. 2. That they were similar, both in degree and kind,t to common meteors. The small number, and absence of a common radiant, support the first position. The nearness to the number frequently seen at a period of the night, and a period of the year when these meteors are less frequent than early in the morning and late in the aotumn, together with the very different points in which their paths, if produced, would have intersected, show the second.

The new facts presented by my friend, Prof. Olmsted, and upon which I now proceed to remark, are classified by him as “foreign testimonies” and "domestic testimonies.”' The first are somewhat particular, but the latter quite general. The foreign testimonies alluded to, are those of the Rev. W. B. Clark, A. M. F. G. S., &c., and W. H. White, Esq., both of England. These gentlemen saw meteors on the morning of the 13th of November, 1834.

The opinion of Mr. Clark in relation to the meteors which he saw, is to be fouod in the same paragraph from which Prof. Olmsted has quoted his

Amer. Journ. Sci. vol. xxv. p. 363. Journ. Frank. Inst. vol. xvi. p. 368, in an art. icle headed Zodiacal Light, between which and the meteors, Prof. 'Olmsted's theory leads him to infer a connexion.

† This term, which I used to denote the peculiarity in regard to the paths of the meteors, has, I find, been misunderstood. I did not mean to express by it an opinion that the meteors of 1835 had a physical cause different from that producing ordinary "shooting stars.” VOL. XVII.—No. 1.- JANUARY, 1836


observations. It is thus expressed: - The coincidence between these and those seen in America and Europe on this day of the month, is curious, but those which I now mention were electrical, and of no uncommon character.* In a subsequent paper, after reviewing the observations made by Prof. Olmsted, Mr. Twining and myself, in America, and by Mr. White and himself in England, the Rev. Mr. Clark thus concludes:f “ One fact is at least established by these seeming contradictions, viz. that common electricali meteors did appear both in America and England, on the same night, whilst there is no direct evidence to show that any others also appeared."

I have considered the opinion of Mr. Clark respecting what he saw, as the more important, because his description of the direction of the meteors is not very precise. He says they were in the direction of a line from Leo to the star Mizar. He may mean that their paths coincided with this line, or merely that they were parallel to it. Taking the former statement as most favourable to the similarity of this phenomena to that of 1833, it would still, however, be very different from that, however remarkable in itself. That fifteen meteors should fall precisely in the same line, is certainly a curious fact, but as certainly a very different one from the apparent convergence to a single point of the paths of more than 207,000 falling in very different parts of the heavens.

The Rev. Mr. Clark further states, that he saw one meteor which appeared to pass to the south of Ursa Major, and between Cor Caroli and Aucturus, the most northern of these stars being about seventeen degrees greater in north polar distance than Mizar. If this was one of the fifteen meteors before alluded to, Mr. Clark probably intended his description to apply to the general direction, and not to the precise position of their paths. This, however, is not important so far as the inference in regard to the question between Prof. Olmsted and myself is concerned.

The greatest number of meteors which Mr. Clark saw was fifteen in fifteen minutes, or else he only observed fifteen minutes; which is the correct supposition his account leaves doubtful. The portion of the heavens his view embraced is also doubtful: he merely states that he observed from a window. To make the hypothesis as favourable as possible to the number of meteors, we may suppose that he observed but for fifteen minutes, and saw fifteen meteors; that his range of vision embraced not more than one-tenth of the visible heavens, and that meteors fell in equal numbers over an equal space in other quarters. All these assumptions, and they are for the most part gratuitous, would make the number over the whole sky six hundred in one hour, while during the display in 1833, six hundred and fifty meteorsø were counted in about one-fourth part of the sky in fifteen minutes, making upwards of 36,000 in one hour, and this only one hour and a quarter before sunrise.

The observations of Mr. White do not seem to me, any more than they do to Mr. Clark, to support the idea of a recurrence of the meteoric phenomenon of 1833. The number of meteors which he saw was ten in half an hour, being less than the number seen in fifteen minutes by Mr. Clark, The observations were made from windows which commanded a view of the north and east, and supposing that they commanded but one-sixth part of the heavens, and that the meteors were of the same frequency in every part,

• Loudon's Mag. Nat. Hist, vol. vii. p. 655. † Ibid. vol. viii. pp. 420, 421.

This term, electrical, is in allusion to his theory. § Amer. Journ. Sci. vol. xxvi. p. 367

« iepriekšējāTurpināt »