SHOOTING STARS

Well-known meteors, of which the origin and nature are involved in great obscurity, and which have, of late years, excited extraordinary interest by their periodical appearances in unusually great numbers. Phenomena of Shooting Stars The apparent magnitudes of these meteors are widely different. The greater part of them resemble stars of the 3d, 4th, 5th, and 6th magnitudes; but some occur which surpa stars of the 1st magnitude, and even exceed Jupiter and Venus in brilliancy. In some of them the globular form can be easily recognized: these are, in every respect, similar to bolides or fire-balls i and, in fact, it is impo ible, from their appearances, to make any distinction between the larger shooting stars and the smaller individuals of the cla of meteors to which the name of fire-balls is usually appropriated. See Fike-balls. Shooting stars appear to be equally numerous in every climate. The weather seems to have no influence upon their number. They are observed at all times of the year; but, generally speaking, they appear to be more abundant in the end of summer and autumn than at the other seasons. Some of the shooting stars leave a luminous train behind them, which marks their path through the sky with a milk-white light. These trains for the most part disappear in a few seconds; but sometimes they contmue longer, and even for several minutes. In the case of actual fire-balls, Dr. Olbers observed trains which continued from six to seven minutes; and Brandes, in one instance, estimated that fifteen minutes elapsed between the extinction of the fire-ball and the disappearance of the luminous train. The trains in general a ume the form of a cylinder, the interior of which is void of luminous matter; and not unfrequently, before their disappearance, they take a curved form. The most probable explanation is, that they are caused by a gaseous matter left behind by the meteor, and bent by currents of air.. The older philosophers had formed various theories to explain these remarkable phenomena. By some they were supposed to be the products of an oily sulphurous vapour existing in the atmosphere, which being disposed in thin layers, and becoming inflamed by some means, would exhibit the appearance of a clear brilliant spark pa ing rapidly from one point to another. About the middle of the last century, when the effects and phenomena of electricity began to be better understood, Beccaria and Va ali, among others, regarded the shooting stars as merely electrical sparks; an hypothesis which was soon shown to be untenable. At a later period, when the inflammable nature of the gases became known, Lavoisier, Volta, Herbert, Toaldo, Gren, and others, referred these meteors to hydrogen gas, which, by reason of its inferior density, they supposed must be accumulated in the higher regions of the atmosphere. Dalton, however, showed that such accumulation cannot take place, inasmuch as all the gases which constitute the atmosphere must be equally diffused through its whole extent, according to the law of Mariotte. Deluc maintained that certain phosphoric exhalations generated in the earth, and becoming inflamed in the sky, formed the true e ence of the shooting stars. In this state the subject remained when Chladni published his celebrated work on the causes of the ma es of iron and other similar substances found in Siberia by Pallas, in which he clearly established, by comparing the circumstances of a great multitude of observations, that the fire-balls are meteors having their origin beyond our atmosphere; that, in fact, they are ma es of nebulous matter moving in space with planetary velocities, which, when they come in the way of the earth in its revolution about the sim, and enter the atmosphere, are inflamed by its resistance and friction, and become luminous, sometimes scattering ma es of stone and iron on the ground. Halley, Wallis, Pringle, Maskelyne, and others, had previously a igned a cosmical origin to these meteors, but without suspecting that ma es of stone and 1113 SHOOTING STARS. iron fell from them. The close resemblance which the greater part of the shooting stars present to fire-balls, at once induced Chladni to consider these phenomena also as cosmical; that is to say, as small ma es of matter not having their origin in our atmosphere, but entering it from without, and which are either entirely consumed in it, or become extinguished when they have pa ed beyond it. These conclusions, however, required to be confirmed by a more accurate investigation of the phenomena; for as yet no exact determination had been made of the actual average heights of the shooting stars above the earth, or of their orbits, velocities, or magnitudes. In the year 1798 this important but difficult inquiry was undertaken by Profe ors Brandes of Leipsig, and Benzenberg of Dii eldorf (both at that time students in Gottingen). Having selected a base line (about nine miles in length), they placed themselves at its extremities on appointed nights, and observed all the shooting stars which appeared, tracing their courses through the heavens on a celestial map, and noting the instants of their appearances and extinctions by chronometers previously compared. The differences of the paths traced on the maps afforded data for the determination of the parallaxes, and consequently the heights and the lengths of the orbits. On six evenings, between September and November, the whole number of shooting stars seen bv both observers was 402; of these 22 were identified as Fiaving been observed by each in such a manner that the altitude of the meteor above the ground at the instant of extinction could be computed. The least of the altitudes was about G English miles. Of the whole there were 7 under 45 miles; 9 between A5 and 90; 6 above 90; and the highest was above 140 miles. There were only two observed so completely as to afford data for determining the velocity. The first gave 25 miles, and the second from 17 to 21 miles in a second. The most remarkable result was, that one of them certainly was observed not to fall, but to move in a direction away from the earth. By these observations a precise idea was first obtained of the altitudes, distances, and velocities of these singular meteors. A similar but more extended plan of observation was organized by Br.indes in 1823, and carried into effect at Breslau and the neighbouring towns by a considerable number of persons observing at the same time on concerted nights. Between April and October.about 1800 shooting stars were noted at the different places; out of which number 62 were found which had been observed simultaneously at more than one station in such a manner that their respective altitudes could be determined, and 36 others of which the observations furnished data for estimating the entire orbits. Of these 98, the heights (at the time of extinction) of 4 were computed to be under 15 English miles; of 15 between 15 and 30 miles; of 22 between 30 and 45; of 33 between 45 and 70; of 13 between 70 and 90; and of II above 90 miles. Of these last two had an altitude of about 140 miles, one of 220 miles, one of 280, and there was one of which the height was estimated to exceed 460 miles. Of the 36 computed orbits, in 26 instances the motion was downwards, in one case horizontal, and in the remaining 9 more or le upwards. The velocities were between 18 and 36 miles in a second. The trajectories were frequently not straight lines, but incurvated sometimes in the horizontal and sometimes in the vertical direction, and sometimes they were of a serpentine form. The predominating direction of the motion of the meteors from north-east to south-west, contrary to that of the earth in its orbit, was very remarkable, and is important in reference to their physical theory. A similar set of observations was made in Belgium in 1824, under the direction of M. Quetelet, the results of which are published in the Anniiaire de Bruxelles for 1837. M. Quetelet was chiefly solicitous to determine the velocity of the meteors. He obtained six corresponding observations from which this element could be deduced, and the results varied from ten to twenty five English miles in a second. The mean of the six results gave a velocity of nearly seventeen miles per second, a little le than that of the earth in its orbit. Another sef of corresponding observations was made in Switzerland on the 10th of August, 1838; a circumstantial account of which is given by M. Wartmann in Quetelet' s Correspond ance Mathematique, for July, 1839. M. Wartmann and five other observers,provided with celestial charts, stationed themselves at the observatory of Geneva; and the corresponding observations were made at Planchettes, a village about sixty miles to the north-east of that city. In the space of seven and a half hours, the number of meteors observed by the six observers at Geneva was 381; and during five and a half hours, the number observed at Planchettes by two observers was 104. All the circumstances of the phenomena — the place of the apparition and disappearance of each meteor, the time it continued visible, its brightne relatively to the fixed stars, whether accompanied with a train, . — were carefully noted, and the trajectories projected on a large [s. 1126]