118 COSMOS. 



must be regarded as almost devoid of air, or occupied by at 

 atmosphere that does not even contain to^oVto"^^ P^'t of oxy 

 gen. The recent investigations of Biot on the important phe 

 nomenon of twilight^ have considerably lowered the lineJi 

 which had, perhaps with some degree of temerity, been usual 

 ly termed the boundaries of the atmosphere ; but processes of 

 light may be evolved independently of the presence of oxygen, 

 and Poisson conjectured that aerolites Avere ignited far beyond 

 the range of our atmosphere. Numerical calculation and geo- 

 metrical measurement are the only means by which, as in the 

 case of the larger bodies of our solar system, we are enabled to 

 impart a firm and safe basis to our investigations of meteoric 

 stones. Although Halley pronounced the great fire-ball of 1686, 

 whose motion was opposite to that of the earth in its orbit, f to 

 be a cosmical body, Chladni, in 1794, first recognized, with 

 ready acuteness of mind, the connection between fire-balls and 

 the stones projected from the atmosphere, and the motions of the 

 former bodies in space. $ A brilliant confirmation of the cos- 

 mical origin of these phenomena has been afibrded by Denison 

 Olmsted, at New Haven, Connecticut, who has shown, on the 

 concurrent authority of all eye-witnesses, that during the cele- 

 brated fall of shooting stars on the night between the 12th 



* Biot, Traiti d' Astronomie Physique (3^me ed.), 1841, t. i., p. 149 

 177, 238, 312. My lamented frieud Poisson endeavored, in a singiilai 

 manner, to solve the difficulty attending an assumption of the sponta- 

 neous ignition of meteoric stones at an elevation where the density of 

 the atmosphere is almost null. These are his words : '• It is difficult to 

 attribute, as is usually done, the incandescence of agrolites to friction 

 against the molecules of the atmosphere at an elevation above the earth 

 vvhere the density of the air is almost null. May we not suppose that 

 the electric fluid, in a neutral condition, forms a kind of atmosphere, ex- 

 tending far beyond the mass of our atmosphere, yet subject to terres- 

 trial attraction, although physically imponderable, and consequently 

 following our globe in its motion ? According to this hypothesis, the 

 bodies of which we have been speaking would, on entering this im- 

 ponderable atmosphere, decompose the neutral fluid by their unequal 

 action on the two electricities, and they would thus be heated, and in 

 a state of incandescence, by becoming electrified." (Poisson, Reck, sur 

 la Probabiliti des Jugements, 1837, p. 6.) 



t Philos. Transact., vol. xxix., p. 161-163. 



X The first edition of Chladni's important treatise, Ueber den Ur^ 

 sprung der von Pallas gefundenen und anderen Eisenmassen (On the 

 Origin of the masses of Iron found by Pallas, and other similar masses), 

 appeared two mouths prior to the shower of stones at Siena, and twc 

 years before Lichtenberg stated, in the Oottingen Taschenbuck, tha 

 " stones reach our atmosphere from the remoter regions of space.' 

 Comp., also, Olbers's letter to Benzenberg. 18th Nov.. 1837, in Ben 



leaberg's Trenfise on Shnotitig Stars, p. ' ^'^ 



