PORTION OF THE COSMOS. AEROLITES. 433 



on the 21st October (Old Style), were the August and 

 November periods which have now moved forward, loses 

 much of its weight by the considerable amount of new 

 experience gained from 1838 to 1848 ( 6 9 8 ). 



November ; 12th to 14th day; very rarely the 8th of 

 10th. The great fall of meteors at Cumana, llth 12th 

 November, 1799, which was described by Bonpland and 

 myself, so far gave occasion to the belief in periodically 

 returning phenomena on determinate days, that when the 

 similarly great meteor-fall of 1833 (Nov. 12th 13th) 

 took place, the phenomenon of 1799 was remem- 

 bered ( 6 9 9 ). 



December : 9th ] 2th ; but, according to Brandes' 

 observation, Dec. 6th 7th, in 1798 ; Herrick, in New- 

 haven, 1838, Dec. 7th 8th; Heis, 1847, Dec. 8th 

 and 10th. 



These eight or nine epochs of periodical streams of me- 

 teors, of which the last five are the best assured, are here 

 recommended to the diligence of observers. Not only do 

 the streams differ from each other in different months, but 

 also the abundance and brightness of the same stream differ 

 strikingly in different years. 



" The upper limit of the height above the Earth of falling 

 stars cannot be accurately made out, and Olbers already 

 regarded all heights of above 30 German, or 120 English 

 geographical miles, as very uncertainly determined. The 

 lower limit, formerly assigned as usually about 16 miles (or 

 upwards of 95000 feet), must be considerably diminished. 

 Some are found by measurement to descend almost as low 

 as the summits of Chimborazo and Aconcagua, or to within 



