14 REPORT — 1861. 



Marsh, in his able notice of the great daylight meteor in the United States, No- 

 vember 15, 1859, affirms, however, that the sowid following the bm-sting of that 

 meteor " was explosive, and not caused hj the falling in of the au- after the meteor, 

 as in the latter case it must have been continuous and interrupted ; but the testimony 

 of Dr. Beesley and others shows that it ceased entirely and then began again. Sup- 

 pose the meteor to have been a stony mass, we may perhaps consider the explosion 

 to have consisted of a series of decrepitations caused by the sudden expansion and 

 heating of the surface. At the forward end these explosions woidd take place under 

 great pressure, which may accoimt for the loudness of the sound." Again, "the 

 explosions were very numerous, the whole occupying only half a second of time ; 

 but the individual soimds were distinguishable because of the difierent distances 

 they had to ti'avel to reach the eai- ; the whole dm-ation of the sound extending ia 

 reality over a minute." 



Tliough I am inclined to agree to a great extent with Mr. Marsh respecting the 

 cause and effects of the soimd being caused by a series of decrepitations taking place, 

 imder pressure of the resisting atmosphere, yet that would hardly explain the sud- 

 den disruption and disappearance of fireball's, actually occm-iing in the majority of 

 cases ; it woidd be too gi-adual a breaking up to accord altogether with facts. 



One obstacle in the way of a satisfactoiy solution arises from the difficulty of 

 ascertaining the real size of an aerolitic fii-eball, which at the distance of 40 mUes 

 or more may appear as large as the moon ; for it has been proved that a very small 

 body, such as a small stone, when in a state of powerful incandescence, appears 

 much larger than it really is ; e. g., Dr. Smith has himself shown that a piece of 

 lime less than half an inch in diameter, in the flame of the oxyhydrogen blowpipe, 

 has, in a clear evening, appeai-ed at the distance of half a mUe to present an appa- 

 rent diameter equal to twice that of the moon ! On the other hand, while this fact 

 seems to afford us facilities for a simple solution, it may still be qiute possible that 

 the stony matter is but a nucleus inside a larger envelope of highly compressed and 

 heated air, containing likewise, as Haidinger supposes and explains, the vacuiun, 

 which subsequently collapses with a loud report. 



It may be here mentioned, that occasionally lai'ge meteore (evidently aerolitic) 

 have been seen to divide into two nearly equal portions (a loud detonation follow- 

 ing some minutes afterwards), and that both have then passed off again into space 

 without other apparent change*. 



It is also equally certain that no noise is heard unless a large fireball actually 

 bm"sts into two or more considerable portions ; and that the principal noise is cer- 

 tainly the dii-ect result of this rupture. How such violent noises and atmospheric 

 concussions as take place are produced and also heard and felt on the surface of 

 the earth is sti-ange, and as yet not fully undei-stood : the height at which fireballs 

 thus burst varies from 15 to 40 mUes. The cases where stones have fallen fi'om fii-e- 

 balls without noise ai'e veiy rare indeed. 



Dr. Lam-ence Smith considers the liffht emitted by fireballs does not arise from 

 mere incandescence, but is caused hj electricity and other causes. M. Haidinger 

 speaks of air heated to whiteness. There must, however, be a certain amount of 

 light ai-ising fi-oni the incandescence of solid matter, judging fi-om the fused crusts 

 of all aerolites, and from the fact of some meteorites, especially iron ones, being 

 known to fall red-hot ; but that at heights of fi'om 20 to 40 or even 100 miles, 

 where the supply of oxygen must be inconceivably small, part of the liglit may be 

 owing to a development of electricity, seems highly probable. 



large meteor ? No noise is ever heard unless the entire fireball is ruptured or flies to pieces. 

 Besides, at elevations of 30 or 40 miles the air woidd be too rarefied to produce much noise 

 from simply rusliing into the space left in the wake of the meteorite. 



* As was the case with the celebrated meteors of August 18, 1783, in England, and that 

 of July 20, 1860, in North America ; which being the fact, goes against M. Haidinger's 

 theory of incandescent air enclosing a vacuum in the rear of the main fireball ; for the 

 bursting would, in the cases just cited, probably have destroyed, at least temporarily, their 

 subsequent visible existence. In these two eases it seems mcst reasonable to suppose that 

 a large stone (several feet in diameter), wliile in a state of high superficial incandescence, 

 "broke" into two parts with a loud crack or report, the sound of which, under the very 

 great jjressure caused by resistance to the atmosphere, would be greatly magnified or in- 

 creased. 



