PROGRESS OF METEORIC ASTRONOMY IN AMERICA. 289 
the naked eye there are 52.7 that are visible through a comet- 
seeker, the whole number of meteoroids coming daily into 
the air is 400,000,000. 
“ 8th. The mean distance of the meteors from the observer 
is less than 144 miles. 
“ 9th. The mean foreshortening of the meteor paths by per¬ 
spective is from 16°.0 to 12°.6. 
“ 10th. The average length of the visible part of meteor 
paths is between 24 and 40 or 21 and 34 miles; probably 
nearer 21 and 34 miles. 
“11th. The mean duration of flight is not* much, if any, 
greater than half a second of time.” 
Prof. II. A. Newton 1 discussed the observations of the al¬ 
titudes of seventy-eight meteors observed on November 13-14, 
1863, at Washington, Haverford College, Germantown, Phil¬ 
adelphia, and other points, giving diagrams exhibiting the 
altitudes of these meteors, and also of thirty-nine meteors 
observed in August, 1863, with the following results: 
November 
meteors. 
Mean altitude at appearance . . 96.2 miles. 
Mean altitude at disappearance . 60.8 “ 
Mean altitude of middle point of 
path .78.5 “ 
August me¬ 
teors. 
69.9 miles. 
56.0 “ 
62.9 “ 
In a paper on “ The Theory of Meteors ” Prof. Daniel Kirk¬ 
wood 2 arrived at the following conclusions : 
“ The zodiacal light is probably a dense meteoric ring, or 
rather, perhaps, a number of rings. 
“ Variable and temporary stars are caused by the interpo¬ 
sition of meteoric rings. 
“ Mercury’s mean motion is probably diminished by the 
action of meteoric matter. 
“ The transit of a meteoric stream or cloud affords the most 
probable explanation of the phenomenon known as ‘ dark 
days.’ 
1 A. J. S., XL 2 , 250. 
2 Proc. A. A. A. S. 1866, 8. 
