METEORIC STONES AND SHOOTING STARS. 



We may, therefore, safely pronounce the atmospheric theory 

 to be incompatible with the ascertained circumstances of the 

 phenomena, and to require admissions inconsistent with the 

 established principles of physics. 



11. The volcanic theory is subject to objections as decisive. The 

 nature of the substances ejected from terrestrial volcanoes is 

 well known, and we do not find among them the substances 

 which form the constituents of meteorites ; besides this, it is 

 found that meteoric stones fall on parts of the earth so remote 

 from volcanoes, and at times so distant from any known 

 extensive eruptions, that it is impossible to admit the sup- 

 position that they have proceeded from this cause. For these 

 and other reasons, needless to dwell on, the volcanic hypothesis 

 is set aside. 



12. The lunar hypothesis has been seriously entertained by 

 many of the most eminent geometers of the last century. Chladni 

 states that the possibility of such an origin of the aerolites was first 

 suggested by Paolo Maria Terzago, an Italian philosopher, in 1660. 

 Unaware of this ancient conjecture, the hypothesis was revived 

 by Dr. Olbers on the occasion of the great fall of meteorites at 

 Sienna, on the 16th of June, 1794. That astronomer in the 

 following year undertook to investigate the force with which 

 such bodies should be projected from a lunar crater, in order to 

 enable them to pass from the sphere of the moon's attraction 

 into that of the earth. The same problem subsequently engaged 

 the attention of Laplace, Biot, Brandes, and Poisson for many 

 years. It was then supposed that, notwithstanding the absence 

 of air and water, active lunar volcanoes existed. 



Some countenance to this idea was derived from a remarkable 

 phenomenon, which several observers affirmed that they had 

 witnessed on the dark disc of the moon in lunar eclipses. They 

 saw, or imagined they saw, vividly bright luminous spots at 

 distances not inconsiderable within the moon's limb. Now 

 such appearances, if real, could only be explained by active 

 lunar volcanoes, or by the very improbable supposition of 

 the existence of holes through the moon through which the 

 sun's light passed. The supposition of any such origin as 

 an aurora borealis was removed by the admitted absence of an 

 atmosphere. 



Laplace, Biot, and Poisson, agreed in their calculations of the 

 velocity with which such bodies must be projected from the 

 moon to reach the earth. This velocity would be about 8000 

 feet per second. But Olbers showed, that although such a force 

 of projection might bring them to the earth, it would not impart 

 to them, on arriving there, a speed greater than 35,000 feet per 

 140 



