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Aerolites. Zio 
because, according to his views, they were simply “ meteors 
arising from the exhalations of the earth, and blending 
with the higher ether.” Others, like Aristotle, considered 
that they were masses of metal raised either by hurricanes, 
or projected by some volcano beyond the limits of the 
earth’s attraction, so becoming inflamed and converted, for 
a time, into star-like bodies. Thirdly, a solar origin; . this, 
however, was freely derided by Pliny, and several others, 
amongst whom we may mention Diogenes of Apollonia, 
already alluded to as one of the chroniclers of the aérolite 
of AXgos Potamos. He thus argues: “Stars that are in- . 
visible, and consequently have no name, move in space to- 
gether with those that are visible..... These invisible 
stars frequently fall to the earth and are extinguished, as 
the stony star which fell burning at A©gos Potamos.” This 
last opinion, it will be seen, coincides, as far as it goes, 
almost exactly with the most modern views on the subject. 
As some of the Greeks derived the origin of meteorites 
from the sun (probably from the fact of their sometimes 
falling during bright sunshine), so we find, at the end of the 
seventeenth century, it was believed by a great many that 
they fell from the moon. This conjecture appears to have 
been first hazarded by an Italian philosopher, named 
Paolo Maria Terzago, whose attention was specially directed 
to this subject on the occasion of a meteoric stone fall- 
ing 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 aérolite at 
Sienna, in the year 1794, he began to examine the question 
by aid of the most abstruse mathematics, 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 aérolites 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 calculation. Biot’s esti- 
