difficulty of securing perfectly accurate observations, the following results must be considered as mere approximations. I. As to the extreme heights during visibility: The average velocity of a considerable number of meteors computed by Prof. A. S. Herschel is 35 miles per second. The estimated diameters of Fireballs are usually much in excess of the real values. The absolute dimensions attributed to several large meteors in the above table must therefore be received with caution. The nucleus of a Fireball during combustion has a flaming aspect, and the glare invariably accompanying it creates an exaggerated impression of its size. Their velocities are also liable to considerable errors, as there are grave difficulties in the way of determining the exact durations of their flights, save in exceptional instances when the speed is slow and the observer is sufficiently prepared for the event to be able to time it carefully. The average heights of Fireballs are less than the average heights of shooting stars. A comparison of many recorded results gives the following relative figures:— It is evident that the brighter forms of meteoric display occur in a lower region of the atmosphere than that of the fainter class of these phenomena. There are certain meteor showers which apparently yield a large proportion of Fireballs. As a very recent example of observations followed by computation the following may be cited. On Nov. 13, 1888, Denning at Bristol and Backhouse at Sunderland each observed a fireball, which on a comparison of the accounts proved to be one and CURIOUS FORM OF TRAIL LEFT BY THE FIREBALL OF OCTOBER 19, 1877. 2 Second effect (10 min. later). the same object. Backhouse states that at 17h 19m he became suddenly aware of a bright flash, and, a few seconds later, he discovered an unusually intense Meteor-streak lying amongst the stars of Boötes and about 5° below Arcturus. It was estimated as 4° long at first, and proved very durable, for it remained in sight for 9m, and exhibited during that time some alteration ! A table of the radiant points of these will be found in the Monthly Not., vol. xliv. pp. 298-9, April 1884. A catalogue of 584 Fireballs is given in Arago's Ast. Pop., vol. iv. pp. 230-79, French Ed. both in shape and position. The places were carefully noted and recorded. Denning's observations were so far less satisfactory in that at Bristol the Meteor was seen much nearer the horizon, but the salient features were so similar that there can be no doubt about the identity of the two objects. TRAIL LEFT BY THE FIREBALL OF NOV. 13, 1888. The details of the observations need not be given, but a summary of them yields the following results: The Meteor's Earth-point was situated in about Lat. N., 55.6°, Long. E., 3.3°, and its radiant at 149°, +25°. The duration of its flight was not estimated, so its velocity cannot be determined. At Bristol however it was described as 'swift,' and the inference is that its motion probably accorded with the usual high rate of speed attributed to the Leonid Meteors. The heights above stated do not differ materially from the average of fireballs, though the length of the path was decidedly shorter than usual 8. Denning, Month. Not., vol. xlix. p. 66, Dec. 1888. CHAPTER III. SHOOTING STARS. Have only recently attracted attention.—Are visible with greater or less frequency every clear night.—Summaries of the monthly and horary rates of apparition from observations by Coulvier-Gravier and Denning.— Number of known meteor showers. Their distribution amongst the constellations.—Monthly number of meteors catalogued.—Early notices of great meteor showers.-The showers of 1799, 1831, 1832, 1833, 1866, and following years.—The shower of Aug. 10.— Of Nov. 27, 1872, and Nov. 27, 1885.-Nomenclature of meteor systems.— Views of Olbers.-Monthly summary of great meteoric displays. SHOC HOOTING stars, although noticed in ancient times, have attracted special attention only during the present century. This branch of the science may therefore be considered to be comparatively in its infancy. Though a vast number of observations have now been accumulated and are available for discussion we require many more, and a searching investigation of the whole subject, before we can claim to have thoroughly mastered its details and to have explained certain peculiarities which are not quite in harmony with prevailing theories. The labours of Heis and Schmidt, of A. S. Herschel and Greg, of Schiaparelli and many others, have however so far smoothed the way to a satisfactory conception of the movements and physical nature of these objects that much of the former mystery concerning them has been cleared away, and we have a substantial basis on which to augment our knowledge". Shooting stars were long considered to have an atmospheric origin and to be due to the combustion of inflammable gases exhaled by the earth. This theory is now rejected in favour of one which is perfectly consistent with the observed features of these a A pamphlet by T. Bredechin entitled Sur l'origine des étoiles filantes, published at Moscow, 1888, may be mentioned in this connection. |