SHOOTING STABS. 583 



* Eight or nine epochs of periodic meteoric streams, of 

 which the last five are most certainly determined, are here 

 recommended to the industry of observers. The streams of 

 different months are not alone different from each other ; 

 in different years, also, the abundance and brilliancy of the 

 same stream varies strikingly. 



" The upper limits of the height of shooting-stars cannot 

 be ascertained with accuracy, and Olbers considers all heights 

 above 120 miles as being less certainly determined. The lower 

 boundaries which were formerly (Cosmos, vol. i. p. 107) gene- 

 rally estimated at 16 miles (over 97,388 feet), must be greatly 

 contracted. Some, according to measurement, descend very 

 nearly to the level of the summit of Chimborazo and Acon- 

 cagua, to the distance of 4 geographical miles above the level 

 of the sea. Heis remarked, on the contrary, a falling star 

 seen simultaneously at Berlin and Breslau on the 10th of 

 July, 1837, had, according to accurate calculation, a height of 

 248 miles when its light first became visible, and a height of 

 168 on its disappearance ; others disappeared during the same 

 night at a height of 56 miles. From the older labours of 

 Brandes (1823), it follows that of 100 well-defined shooting- 

 stars seen from two points of observation, 4 had an elevation 

 of only 4 to 12 miles; 15 between 12 and 24 m.; 22 from 24 

 to 40 ; 35 (nearly one-third) from 40 to 60 m. ; 13 from 40 to 

 80 m. ; and only 1 1 (scarcely one-tenth) above 80 m. their 

 heights being between 180 and 240 miles. From 4000 obser- 

 vations collected during nine years, it has been inferred with 

 regard to the colour of the shooting-stars, that two-thirds 

 are white, one-seventh yellow, one-seventeenth yellowish red, 

 Vid only one-thirty-seventh green." 



Olbers reports, that during the fall of meteors in the night 

 of the 12th and 13th of November, in the year 1838, a beau- 

 tiful northern light was visible at Bremen, which coloured 

 parts of the sky with an intense blood-red light. Tho 



