Outlines of Meteoric Astronomy. 213 



England since the night of November 12th — 13th, 1832., 

 when it is related the horses of the mail between York 

 and Richmond were terrified by the brightness of the 

 meteors. Shoofcing-stars are now better observed, by await- 

 ing their arrival every year upon the 10th of August, than 

 they could have been at any former period of their history. 

 Star-showers also return (but not regularly) on the 2nd 

 January; 9th— 10th, and 20th— 26th April; 25th— 30th July ; 

 15th — 23rd October; and 6th — 12th December ; with their 

 radiant points respectively at v Herculis, S Virginis, a Lyras, 

 7 Cygni, v Orionis, and 6 Geminorum. 



(6.) On the 10th of August, 1863, the tracks of twenty 

 meteors were observed at the English national observatories in 

 such a manner as to determine their heights and velocities with 

 precision. On comparing these results with nearly two hundred 

 instances formerly observed, a remarkable uniformity is dis- 

 covered, and it may be stated on an average, with an error of 

 not more than two or three miles, that shooting-stars, from the 

 smallest visible to those as bright as the planets, appear at 

 seventy-three, and disappear at fifty-two miles above the sur- 

 face of the earth. Either a different composition must pre- 

 vail in the second forty miles of the earth's atmosphere to 

 account for this remarkable uniformity (perhaps the fluid which, 

 according to Mr. Airy, occasions magnetic storms), or else we 

 must admit that shooting- stars, whatever their size and splen- 

 dour, are composed of such fragile materials, that they are all 

 alike dissipated by an equal opposition of resistance. The lower 

 portion of forty miles is generally called the crepuscular atmos- 

 phere from its giving rise to the phenomenon of twilight. The 

 upper portion of forty miles might, in the absence of any other 

 name, be termed the meteoric atmosphere, because it generates 

 the light of meteors, but M. Quetelet assigns the names of 

 stable and unstable to the upper and lower portions of the 

 atmosphere. 



(7.) Not only periodical meteors, but also ordinary shooting- 

 stars, which may be observed in small numbers every night, 

 are shown to belong to showers, many of which at present are 

 as well determined as of those of August and November. 

 They return with their attendant radiant points, without con- 

 fusion or chance, at regular seasons of the year. Although 

 not so rich in meteors, they are even more regular in their re- 

 turn, more constant and long enduring than the extraordinary 

 occurrences of star-showers. The latter are evidently groups 

 in circulation round the sun, but the meteors of August 

 must compose a narrow ring encompassing the sun, for 

 otherwise they could not return, on one and the same date, 

 regularly every year, with only a single interruption, 



