358 M. Haidinger on the Phenomena attending 



inclined to overrate the size of an object, the reports or accounts 

 of fireballs showing a half or the whole of the full-moon's dia- 

 meter, when seen from a distance of 20, 40, 60, or 100 miles, 

 cannot, however, entirely rest on self-delusion*. A large space 

 may be occupied by the igneous globe, surrounding a far smaller 

 nucleus, consisting of one or more fragments. 



On coming with enormous velocity from planetary space into 

 our atmosphere, the acoustic phenomenon may be accounted for 

 by supposing that the fireball includes, as we have attempted to 

 explain, a real vacuum maintained by the resistance of the atmo- 

 sphere against it. The original velocity having at length been 

 sufficiently retarded by the air, the meteor becomes almost sta- 

 tionary ; at this moment the vacuum suddenly collapses in the 

 already rather dense air, and detonation ensues from reper- 

 cussion of the air filling up the vacuum. The intensity of the 

 sound ceases to be a matter of wonder when we consider the 

 explosions caused by setting fire to bubbles filled with oxy-hy- 

 drogen gas suspended in the air. The so-called " consecutive 

 explosions," or series of smaller detonations, may depend on the 

 more or less gradual dimiuution of the cosmical velocity f. 



Hitherto only one solid body has come into question. When, 

 however, meteorites arrive in flocks or groups, as when 3000 

 stones (the largest 17 lbs.) fell from a detonating meteor at 

 I/Aigle in France, on the 26th of April, 1803, nearly 200 at Stan- 

 nern in Moravia, 22nd May, 1808, and some 30 or 40 near New 

 Concord, Ohio, on May 1st, 1860, it may be supposed that even 

 if one principal explosion " had commenced the action," subse- 

 quent detonations of the several isolated portions could likewise 

 have taken place. I do not, however, believe that in the above- 



* The meteor of Feb. 11, 1850, seen in England at a distance subse- 

 quently calculated at 50 miles, appeared, as at Hartwell, as large as the full 

 moon; at places 100 miles distant from its vertical passage, as large as 

 Venus. That of July 20, 1860, seen in the United States, had a decided 

 apparent diameter nearly equal to that of the full moon, when at a height 

 of 41 miles. That of October 18, 1783, at a height of 60 miles, over Lin- 

 colnshire, presented a similar appearance.— R. P. G. 



t It may be here fair to mention that Mr. Benj. W. Marsh, of the United 

 States, considers (in his Report in the Journal of the Franklin Institute, on 

 the daylight meteor of Nov. 15, 1859, seen in New Jersey) that the aerolitic 

 detonation arises from a series of decrepitations caused by the sudden expan- 

 sion of the surface of the stony fragment, the whole time of flight not being 

 sufficient to penetrate the mass. At the forward end these explosions would 

 take place under great pressure, which might account for the loudness of 

 the sound. The force of these explosions, directed backwards, would like- 

 wise tend to check the forward velocity of the mass. He also considers 

 that the audible explosion, often lasting several minutes, is the result of the 

 actual bursting of the meteor; for though the explosion might only occupy 

 in reality half a second of time, yet in that interval the noise might be 

 distributed over a distance of twenty or thirty miles. — R. P. G. 



