XX11 NOTES. 



aerolites. The ancients had also a strange fable (Dio Cassius, kxv. 1259) of 

 silver which fell from heaven, and with which it was attempted, under the 

 Emperor Severus, to silver over bronze coins : the presence of metallic iron in 

 meteoric stones was, however, known (Plin. ii. 56). The frequent expression, 

 "h^pidibus pluit," must not, however, be always interpreted to mean falls of 

 aerolites. In Liv. xxv. 7, it probably refers to erupted pumice (rapilli), from 

 the then not quite extinct volcano Mons Albanus (Monte Cavo) ; see Heyne, 

 Opuscula Acad. T. iii. p. 261 ; and my Relat. Hist. T. i. p. 394. The con- 

 flict of Hercules with the Lygians, on the way from the Caucasus to the 

 Hesperides, belongs to a different set of ideas : it is an attempt to explain 

 mythically the origin of the round quartz blocks in the Lygian field of stones 

 at the mouth of the Rhone, which Aristotle supposed to have been ejected from 

 fissure during an earthquake, and Posidonius ascribes to the action of 

 the waves of an inland sea. In the fragment of the Prometheus Freed of 

 jEsehylus, there is a proceeding which closely resembles a fall of aerolites. 

 Jupiter draws together a cloud, and " covers the ground with rounded stones 

 for rain." Posidonius allowed himself to laugh at the geological mythus of 

 stones and blocks. The Lygian field of stones is, however, very naturally and 

 faithfully described. The district is now called La Crau. (Vide Guerin, 

 Mesures barometriques dans les Alpes et Meteorologie d' Avignon, 1829, Ch. xii. 

 p. 115). 



(^ p. 109. The specific gravity of aerolites varies from 1'9 (Alais) to 4'3 

 (Tabor). The most usual density is 3, water being 1. In regard to the actual 

 diameters of fire-balls, the numbers in the text refer to the few tolerably 

 certain measurements which can be collected. These give for the fire-ball of 

 Weston, in Connecticut, 14th of December, 1807, only 500 feet; for the one 

 observed by Le Roi, 10th of July, 1771, about 1000 feet ; and for the one of 

 the 18th of January, 1713, (estimated by Sir Charles Blagden), 2600 feet 

 diameter. Brandes gives to shooting stars a diameter of 80 120 feet, with 

 luminous trains of 3 or 4 (12 or 16 Engl.) miles in length, (Unterhalt. Bd. i, 

 S. 42). There are not, however, wanting optical reasons which render it 

 probable that the apparent diameters of fire-balls and shooting stars have been 

 greatly over-estimated. The volume of the largest which has been seen 

 cannot properly be compared to the volume of Ceres, (should we even assign 

 to that planet a diameter of only 70 English miles). Vide the generally 

 so exact and excellent treatise on the Connexion of the Physical Sciences, 

 1835, p. 411. To elucidate what I have said, in page 110, of the large 

 aerolite which fell in the bed of the river near Narni, but which has not been 



