AEROLITES. 109 



depends upon a number of conditions whose accidental coin- 

 cidence could alone convert a possible into an actual fact. 

 The view of the original existence of small planetary masses 

 in space is simpler, and at the same time more analogous 

 with those entertained concerning the formation of other 

 portions of the solar system. 



sistance of the air, an initial velocity of 8292 feet in the second ; ao 

 cording to Laplace, 7862; to Biot, 8282; and to Poisson, 7595. 

 Laplace states that this velocity is only five or six times as great as 

 that of a cannon-ball, but Olbers has shewn, " that with such an initial 

 velocity as 7500 or 8000 feet in a second, meteoric stones would arrive 

 at the surface of our earth with a velocity of only 35,000 feet, (or 1'53 

 German geographical mile.) But the measured velocity of meteoric 

 stones averages 5 such miles, or upwards of 114,000 feet to a second; 

 and consequently the original velocity of projection from the Moon must 

 be almost 110,000 feet, and therefore 14 times greater than Laplace 

 asserted." (Olbers, in Schum. Jahrb., 1837, pp. 52-58 ; and in Gehler, 

 Nues physik. Worterbuche, bd. vi. abth. 3, s. 2129-2136.) If we 

 could assume volcanic forces to be still active on the Moon's surface, 

 the absence of atmospheric resistance would certainly give to their 

 projectile force an advantage over that of our terrestrial volcanoes ; but 

 even in respect to the measure of the latter force (the projectile force of 

 our own volcanoes), we have no observations on which any reliance can 

 be placed, and it has probably been exceedingly over-rated. Dr. Peters, 

 who accurately observed and measured the phenomena presented by 

 yEtna, found that the greatest velocity of any of the stones projected from 

 the crater was only 1250 feet to a second. Observations on the Peak of 

 Teneriffe, in 1798, gave 3000 feet. Although Laplace, at the end of his 

 work (Expos, du Syst. du Monde, ed. de 1824, p. 399), cautiously 

 observes, regarding aerolites, " that in all probability they come from 

 the depths of space ;" yet we see from another passage (chap. vi. p. 233), 

 that, being probably unacquainted with the extraordinary planetary 

 velocity of meteoric stones, he inclines to the hypothesis of their lunar 

 origin, always, however, assuming that the stones projected from the 

 Moon " become satellites of our Earth, describing around it more or less 

 eccentric orbits, and thus not reaching its atmosphere until several 

 or even many revolutions have been accompHshed." As an Italian at 

 Tortona had the fancy that aerolites came from the Moon, so some of 

 the Greek philosophers thought they came from the Sun. This was 

 the opinion of Diogenes Laertius (ii. 9), regarding the origin of the 

 mass that fell at JSgos Potamos (see note, p. 103). Pliny, whose labours 

 in recording the opinions and statements of preceding writers are 

 astonishing, repeats the theory, and derides it the more freely, because 

 he. with earlier writers (Diog. Laert., 3 and 5, p. 99, Hiibner), accuses 

 Anaxagoras of having predicted the fall of aerolites from the Sun : 

 " Celebrant Graeci Anaxagoram Clazomenium Olympiadis septuagesimae 

 octavae secundo anno praedixisse caelestium litterarum scientia, quibua 

 die bus sax urn casurum esse e sole, idque factum interdiu in Thraciaa 



