AEKOLITES. 
411 
the occasion of a meteoric stone falling at Milan in 1660, and 
killing a Franciscan monk. Olbers, however, was the first to 
treat this theory in a scientific manner, and soon after the 
fall of an aerolite at Sienna, in the year 1794, he began to 
examine the question by the aid of the most abstruse mathe- 
matics, and after several years* labour he succeeded in showing 
that, in order to reach our earth, a stone would require to start 
from the moon at an initial velocity of 8,292 feet per second ; 
then proceeding downwards with increasing speed, it would 
arrive on the earth with a velocity of 35,000 feet per second. 
But as frequent measurements have shown that the actual 
rate of aerolites averages 114,000 feet, or about 21 \ miles per 
second, they were proved by these curious and most elaborate 
calculations to have come from a far greater distance than that 
of our satellite. It is but fair to add that the question of 
initial velocity, on which the whole value of this, so-called, 
“ Ballistic problem/* depends, was investigated by three other 
eminent geometricians, Biot, Laplace, and Poisson, who during 
ten or twelve years were independently engaged upon this cal- 
culation. Biot*s estimate was 8,282 feet in the second ; 
Laplace, 7,862; and Poisson, 7,585, — results all approxima- 
ting very closely with those stated by Olbers. 
We have already observed, at the beginning of this paper, 
that meteoric stones may fall at any moment, but observations, 
extending over many years, have sometimes been brought 
forward to show that, as far as locality is concerned, all coun- 
tries are not equally liable to these visitations. In other 
words, the large number of aerolites which have been known 
to fall within a certain limited area, has been contrasted with 
the apparent rarity of such occurrences beyond these limits. 
If it could be proved that the earth possessed more attractive 
power in some places than in others, this circumstance might 
be satisfactorily explained, but in default of any such evidence, 
the advocates of this theory must rely solely upon statistics, 
which from their very nature require to be taken with a 
certain amount of reserve. Professor Shepard, in Silliman’s 
American Journal , has remarked that “ the fall of aerolites is 
confined principally to two zones; the one belonging to 
America is bounded by 33° and 44° north latitude, and is 
about 25° in length. Its direction is more or less from north- 
east to south-west, following the general line of the Atlantic 
coast. Of all known occurrences of this phenomenon during 
the last fifty years, 92‘8 per cent, have taken place within 
these limits, and mostly in the neighbourhood of the sea. 
The zone of the eastern continent — with the exception that it 
extends ten degrees more to the north — lies between the 
same degrees of latitude, and follows a similar north-east 
vol. v. — no. xxi. 2 r 
