100 COSMOS, 



etars fall as if from a height of twelve or fifteen thousand feet* 

 that they were of brighter colours and left a more brilliant 

 line of light in their track, but this impression was no doubt 

 owing to the greater transparency of the tropical atmo- 

 sphere,* which enables the eye to penetrate further into dis- 



* Relation Historigue, t. i. pp. 80, 213, 527. If in falling stars, as in 

 comets, we distinguish between the head or nucleus and the tail, we shall 

 find that the greater transparency of the atmosphere in tropical climates 

 is evinced in the greater length and brilliancy of the tail which may be 

 observed in those latitudes. The phenomenon is therefore not necessarily 

 more frequent there, because it is oftener seen and continues longer 

 visible. The influence exercised on shooting stars by the character of 

 the atmosphere is shewn occasionally even in our temperate zone, and at 

 very small distances apart. Wartmann relates that on the occasion of a 

 November phenomenon at two places lying very near each other, Geneva 

 and Aux Planchettes, the number of the meteors counted were as 1 to 7. 

 (Wartmann, Mem. sur les Etoilesfilantes, p. 17.) The tail of a shooting 

 star (or its train), on the subject of which Brandes has made so many exact 

 and delicate observations, is in no way to be ascribed to the continuance 

 of the impression produced by light on the retina. It sometimes continues 

 visible a whole minute, and in some rare instances longer than the light 

 of the nucleus of the shooting star ; in which case the luminous track 

 remains motionless. (Gilb. Ann., bd. xiv. s. 251.) This circumstance- 

 further indicates the analogy between large shooting stars and fire balls. 

 Admiral Krusenstern saw, in his voyage round the world, the train of a 

 re ball shine for an hour after the luminous body itself had disappeared, 

 and scarcely move throughout the whole time. (Reise, th. i. s. 58.) Sir 

 Alexander Burnes gives a charming description of the transparency of 

 the clear atmosphere of Bokhara, which was once so favourable to the 

 pursuit of astronomical observations. Bokhara is situated in 39 43' N. L. y 

 and at an elevation of 1280 feet above the level of the sea. " There is a 

 constant serenity in its atmosphere, and an admirable clearness in the sky. 

 At night, the stars have uncommon lustre, and the milky way shines glo- 

 riously in the firmament. There is also a never-ceasing display of the 

 most brilliant meteors, which dart like rockets in the sky : ten or twelve 

 of them are sometimes seen in an hour, assuming every colour ; fiery red, 

 blue, pale and faint. It is a noble country for astronomical science, and 

 great must have been the advantage enjoyed by the famed observatory of 

 Samarkand." (Burnes, Travels into Bokhara, vol. ii. (1834,) p. 158.) A 

 mere traveller must not be reproached for calling ten or twelve shooting 

 stars in an hour, " many." since it is only recently that we have learnt, 

 from careful observations on this subject in Europe, that eight is the 

 mean number which may be seen in an hour in the field of vision of one 

 individual (Quetelet, Corresp. Mathem., Novem. 1837, p. 447); thU 

 number is, however, limited to five or six by that diligent observer, 

 flftere. (Schuir.. Jahrb., 1838, s. 325.) 



