Marsh.] iZU [March 6, 



collision or oscillation of neighboring atoms of matter, will thus have 

 disappeared : but latent heat, in the quantity of condensed ether or re- 

 pulsive force, ready to be developed on the renewed approach of the 

 atoms, will have reached its maximum, and may be capable of producing 

 the most splendid igneous phenomena, like the northern lights or tropi- 

 cal thunder storms." 



Quetelet, in view of the phenomena peculiar to the upper air, proposed 

 to consider it as a distinct atmosphere, and says* "This upper atmos- 

 phere, favorable to the combustion and brilliance of shooting stars, would 

 not necessarily be of the same nature and the same composition, as the 

 lower atmosphere in which we live." 



Sir John Herschel also seems to recognize something not unlike what 

 I have suggested, when, in writing to Quetelet of shooting stars, in 

 August, 1863, he says,f "As to their great elevation above the earth, it 

 leads us to suspect the existence of d kind of atmosphere higher up than 

 the aerial atmosphere, lighter, and, so to s^Deak, more igneous than our 

 own." 



The train of reasoning which I have suggested leads to the conclusion 

 that this "more igneous " condition commences at a height of forty or 

 fifty miles, and extends to the utmost limit of the atmosphere ; its in- 

 tensity increasing with the height in a geometric ratio — the outer shell 

 of air being so completely saturated with heat, that, like a sponge filled 

 with water, it responds to the slightest pressure. It is evident that this 

 fiery envelope may prove a most efficient shield to protect us from the 

 effects of collision with all sorts of fragmentary missiles which the earth 

 may encounter in its journeys around the sun ; and the proof of its 

 efficiency is found in the fact that of the immense number of meteors 

 visible, only a very few have been known to reach the earth. 



Fortunately, the enormous velocity^ — vastly exceeding that of the 

 swiftest cannon ball — with which these missiles are hurled at us, usually 

 causes their almost instantaneous destruction. 



Were they simply dropped from |^ or ^ of the height, falling with the 

 velocity due to the earth's attraction only, it is probable that every one of 

 any appreciable weight, would reach the earth. Without this protecting 

 envelope, we might well dread the effects of such a bombardment as was 

 witnessed in Italy on the 27th November, 1873, wben we encountered 

 some of the debris of Biela's Comet, and when the number of meteors 

 seen by the Italian Astronomers in the course of a few hours was estima- 

 ted by them at near forty thousand. 



The fact seems to be, that the planetary velocity with which a meteor 

 enters our atmosphere, soon causes it to develop, by compressing the air 

 before it — heat sufticient to vaporize its surface layer, and, to communi- 

 cate to it the most dazzling brightness. Time not being allowed for the 



♦Meteors, Aerolites, Storms and Atmospheric Phenomena. From the French of 

 Zilrcher and Margolle, by Wm. Liickland. New York, 1870, p. 229. 



tBulletins of the Royal Academy of Brussels, vol. XVI., p. 320. 



