the needle would appear equally attracted above and below; therefore, in spite of appearances, there was a real decrease. This diminution of the magnetic force with the elevation seems likewise to result from the observations made in 1829, on the summit of Mount Elbrouz (in the Caucasus), by M. Kupffer. In this case an exact account was taken of the effects of temperature, and yet various irregularities in the series of inclinations threw some doubt on the result.

We conceive, therefore, that comparisons of the magnetic intensity, at bases and at summits of mountains, ought to be particularly recommended to the officers of the Bonite. Mowna-Roa, in the Sandwich Islands, seems to be well adapted for the purpose. Observations may likewise be made on the Tacora, if the expedition stop for a few days. at Arica.


ON LIGHTNING.-M. Fusinieri has been lately studying the effects of lightning under an entirely new point of view.

According to this physicien, the electrical sparks issuing from ordinary machines, which we see as they traverse the air, contain brass in a state of fusion, and incandescent molecules of zinc, when they emanate from a brass conductor; if the sparks issue from a ball of silver they contain impalpable particles of that metal. In the same way, a globe of gold gives rise to sparks, which contain, during their passage through the air, melted gold, &c. &c.

The molecules in the centre only of all these sparks are melted; on their exterior surfaces the metallic particles undergo a greater or less degree of combustion, in consequence of their contact with the oxygen of the atmosphere.

When a spark issuing from a globe of gold passes through a silver plate, even of considerable thickness, there is seen on the two surfaces of the plate, at the points where the electric spark entered and emerged, a circular stratum of gold, the thickness of which must be very

inconsiderable, since, if left to itself, it volatilizes, and disappears entirely in a short time. According to M. Fusinieri, these two metallic spots are formed by the fused gold which the electric spark contained. The deposit on the first face is nothing extraordinary; but, by adopting the explanation of the Italian physicien for the spot on the opposite surface, we are obliged to admit, that the gold disseminated through the spark has passed, at least in part, along with it through the whole thickness of the silver plate! It is unnecessary to add, that a spark issuing from a ball of copper gives rise to similar phenomena.

A spark emanating from one metal, and passing through another, does not only lose a portion of the molecules with which it was at first charged, but it acquires new molecules at the expense of the metal traversed. M. Fusinieri even asserts, that, at each passage of the spark, reciprocal changes are produced between the two metals present; that when the spark, for example, leaves silver to pass to copper, it not only transports a portion of the first metal to the second, but that it likewise transports copper to the silver! I will insist no longer, however, on


these phenomena ; I have cited them here only with a view to show that the sparks of our ordinary machines contain ponderable matter.

M. Fusinieri affirms that similar matter exists in lightning, and that in this case also it is in states of minute division, of ignition, and of combustion. According to him, this transported matter is the true cause of the transient smells which thunder occasions when it falls, and also of the pulverulent deposits which remain round fractures through which the electrical matter has forced a passage. In these deposits, which have been too much neglected hitherto by observers, M. Fusinieri has detected metallic iron, iron in different degrees of oxidation, and sulphur. The ferruginous spots left on the walls of houses may be found, when strictly examined, to arise from the iron with which the lightning was charged, derived from that which occurs in every building; but what is to be said regarding the sulphureous spots on these same walls, and especially the ferruginous marks which are found on trees struck with lightning in the open fields ? M. Fusinieri conceives himself authorized to infer from these experiments, that the atmosphere contains, at every height, or at least as far as the region of stormy clouds, iron, sulphur, and other substances, on the nature of which chemical analysis has been hitherto silent ; that the electrical spark is charged with them, and that it carries them to the surface of the earth, where they form attenuated deposits round the points struck with the lightning.

This new method of regarding electrical phenomena, assuredly deserves to be followed up with that accuracy which is suited to the present state of science. Every one who witnesses a stroke of lightning, would perform a very useful service by carefully collecting the black or coloured matter which the electrical fluid seems to deposit, at all those stages of its progress where it undergoes sudden changes of velocity. A careful chemical analysis of these deposits may lead to unexpected discoveries of high importance.

FALLING STARS.-Ever since observations were made with accuracy on falling stars, it has been evident how greatly these long-despised phenomena,—these pretended atmospheric meteors,—these so-called trains of inflamed hydrogen gas, are deserving of attentive examination. Their parallax has already placed them much higher than the sensible limits given to our atmosphere by received theories*. During the inquiry concerning the apparent direction in which these falling stars ordinarily move, it was ascertained that even though they are inflamed in our atmosphere, they do not originate in it, but that they enter it from without. The direction most common to them, seems diametrically to be opposed to that of the earth in its orbit!

It is desirable that this result should be established by the investi* Comparative observations made in motion round the sun. Even although 1823 at Breslau, Dresden, Leipsic, Brieg, we were inclined to regard half of this apand Gleiwitz, by Professor Brandes and parent velocity as an illusion arising from many of his pupils, have assigned no less the effect of the earth's movement in its than 500 English (miles as the height of orbit, there would still remain 18 miles per certain falling stars.

second as the real velocity of the star, a The apparent speed of these meteors is degree of rapidity which exceeds that of all found sometimes to be 36 miles per second. the superior planets, except the earth. This is nearly double that of the earth's

gation of a numerous series of observations. We have therefore requested that officers on watch on board the Bonite may note, during the whole of the voyage, the hour at which a falling star may appear, its probable angular height above the horizon, and particularly, the direction of its motion,

By referring these meteors to the principal stars of the constellations which they traverse, the different questions which we have indicated may be resolved at a glance. Here, then, is a subject of research which requires no trouble. It may suffice to attach our young countrymen to the subject, to remark how interesting it would be to establish the fact of the earth being a planet, from proofs derived from such phenomena as falling stars, the inconstancy of which has become proverbial. We might add, if it were necessary, that it is scarcely possible at present to imagine any other mode of explaining the astonishing appearance of bolides (fiery meteors) observed in America on the night of the 12th and 13th of November, 1833, than by supposing that, besides the large planets, there move round the sun myriads of small bodies which are not visible but when they penetrate into our atmosphere, and there become inflamed; that these asteröids (to adopt the name which Herschel long since applied to Ceres, Pallas, Juno, and Vesta,) move in some way or other in groups; that others, however, are isolated; and that the assiduous observation of these falling stars will be, at all times, the only means of enlightening us in regard to these curious phenomena.

We have just mentioned the appearance of falling stars noticed in America in 1833. These meteors succeeded each other so quickly, that they could not be counted; but a moderate calculation makes their number amount to hundreds of thousands *. They were seen along the eastern side of America from the Gulf of Mexico to Halifax, from nine o'clock in the evening to sunrise, and even, in some places, in daylight, at eight o'clock in the morning. All these meteors issued from the same point of the sky, situate near y Leonis ; and that, notwithstanding the altering position of this star in consequence of the diurnal movement of the sphere. This, then, is assuredly a very remarkable fact, and we shall cite another which is not less so. The shower of falling stars in 1833 took place, as we have already said, on the night of the 12th and 13th of November. In 1799, a similar shower was observed in America, by M. von Humboldt; in Greenland, by the Moravian fraternity; and in Germany, by various persons. The date is in the night between the 11th and the 12th of November,

* The stars were so numerous, and ap- | visible horizon. This number, in his opipeared in so many different regions of the nion, was not more than two-thirds of the sky at once, that in the attempt to reckon whole; thus there must have been 866, them, nothing more than a very rough ap- and in the whole of the visible hemisphere, proximation could be expected. An ob- 8660. This last number would give 34,640 server at Boston compared them, when at stars per hour. As the phenomenon lasted the maximum, to half the number of flakes seven hours, the number that appeared at seen in the air during an ordinary fall of Boston must have exceeded 240,000; for

At a time the phenomenon was it must not be forgotten that the data on considerably on the decrease, he counted which these calculations are founded, were 650 stars in 15 minutes, although he cir- not collected till the phenomenon was concumscribed his observations to a zone, siderably on the decline. which did not include a tenth part of the


In 1832 Europe, Arabia, &c., were witnesses of the same phenomenon, but on a smaller scale. The date of this appearance is again the night between the 12th and the 13th of November.

This near approach to identity in the dates, authorizes us the more to invite our young navigators to watch attentively whatever may appear in the sky from the 10th to the 15th of November, since observers who were favoured with a clear atmosphere, and who watched for the phenomenon last year (1834), saw manifest traces of it on the 12th and 13th of that month*.

THE ZODIACAL LIGHT.-The zodiacal light, although known for nearly two centuries, still presents a problem which has not been solved in a satisfactory manner. The study of this phenomenon is chiefly reserved, by the very nature of things, to observers placed in the equinoctial regions. They alone can decide whether Dominico Cassini had sufficiently guarded against the causes of error to which an observer is exposed in our variable climates, and whether he had sufficiently taken into account the purity of the air, when he announced in his work that the zodiacal light is constantly brighter in the evening than in the morning; that in the course of a few days its length may vary from 60° to 100°; that these variations are connected with the appearance of solar spots, in such a manner, for instance, that there must have been an absolute relation, and not merely a fortuitous coincidence, between the weakness of the zodiacal light in 1688, and the absence of every kind of spot, luminous or otherwise, on the solar disc in that same year.

It appears to us, therefore, that the Academy ought to request the officers of the Bonite, during the whole time they remain between the tropics, and when the moon does not enlighten the horizon, to be on the watch, either after sunset or before sunrising, and take note of the constellations which the zodiacal light traverses, of the star nearest its point, and of the angular breadth of the phenomenon near the horizon, at a determined height. It is almost superfluous to add, that an account must be kept of the hours when the observations were made. The investigation of the results may be delayed without any inconvenience till the period of returning home.

Since my report was read to the Aca- | Lille by M. Delezenne. It left behind on demy, M. Berard, one of the best informed its route, a train of sparks in every respect officers in the French navy, has had the resembling those produced by a squib. kindness to address to me the following Thus, all these facts tend more and more extract from the journal of the brig Loiret, to confirm the notion, that there exists of which he was the commander:

a zone composed of millions of small bodies, “On the 13th November 1831, at 4 whose orbits meet the plane of the ecliptic o'clock A, M., the sky being perfectly clear, near the point which the earth occupies with abundance of dew, we saw a consider- every year, from the 11th to the 13th of able number of falling stars, and luminous November. It is a new planetary world meteors of a large size, For upwards of just beginning to be revealed to us. three hours there could not, on an average, It is doubtless unnecessary for me to be fewer than two every minute. One of say, how important it wonld be at the prethese meteors, which appeared in the zenith, sent moment to inquire whether other left an enormous train in a direction from trains of asteröids do not meet the ecliptic east to west, and formed a broad luminous in points different to that in which the earth band (equal to half the diameter of the is placed about the 13th of November. moon), in which many of the colours of This investigationwould require to be made, the rainbow were very distinctly seen. for example, from the 20th to the 24th of Its track was visible for more than six April; for in 1803 (I believe it was on the minutes. We were then on the coast of 22nd of April), there were seen in Virginia Spain, near Carthagena ; the thermometer and Massachusetts, from one o'clock till in the air, 62:6° Fahr.; barometer, 30•3 three in the morning, falling stars in all in. ; temperature of the sea, 65•2o.” directions, and in such numbers, that they

On the 13th November 1835, a large ight be compared to a shower of rockets. and brilliant meteor observed by M. Millet Messier relates that, on the 17th June Daubenton, fell near Belley, in the 1777 about noon, he saw during five department of Ain, and burned a barn. minutes a prodigious number of black On the same night a falling star, more globules passing across the sun.

Might brilliant than Jupiter, was observed at not these globules be asteröids likewise ?

We are not ignorant, and we have already hinted it, that some very able minds consider these statements of Dominico Cassini as little deserving of confidence. They are unwilling to admit that sensible physical changes could operate simultaneously through such an immense extent as the zodiacal light embraces. In their opinion, these variations in intensity and length, noticed by this great astronomer, were not real, and nothing further than intermissions of the atmospheric transparency are required to account for them.

It would not now, perhaps, be impossible to prove, by comparing the observations of Fatio with those of Cassini, that atmospheric variations are insufficient to explain the phenomena described by the Parisian astronomer. With respect to the objection derived from the immensity of the space in which the physical changes must operate, it has lost all its force since we have witnessed similar phenomena exhibited by Halley's comet. Our

young countrymen ought therefore zealously to devote themselves to such observations as we have pointed out. The question is important, and no person can hitherto flatter himself with having definitively solved it.

AURORA BOREALIS. It is now well ascertained that there are as many displays of polar aurora in the southern hemisphere as in the arctic regions. Everything leads us to think, that the appearances of the southern aurora, and of that which we witness in Europe, follow the same laws. This, however, is mere conjecture. If a southern aurora be seen by the officers of the Bonite in the form of an arch, it will be important to notify exactly the bearings of the intersections of this arch with the horizon, and, if these cannot be obtained, the bearing of the most elevated point. In Europe, the most elevated point always appears to be situated in the magnetic meridian of the place where the observer is stationed.

It has been proved by numerous researches undertaken at Paris, that all kinds of aurora borealis, even such as do not appear above our horizon, and the existence of which, consequently, we can learn only from the reports of observers in the polar regions, alter decidedly the declination of the magnetic needle, as well as its inclination and intensity. Who, then, can presume to argue from the great distance of an aurora australis, that it never disturbs the magnetism of our hemisphere? Every case in which the attention of our travellers shall make a correct memorandum of these phenomena, may at length throw some light on the question. Such arrangements have been made, that magnetic observations will be made at Paris during the whole time of the circumna


[ocr errors]
« VorigeDoorgaan »