NOTES ON Tlin: HATH FURNACE AEROLITE. 199 



they enclose and conceal. The size and the brightness of this trail 

 of fiery sparks is indicative of the immense erosion and reduction 

 which the solid meteorite is undergoing. The greater size of the 

 front or head of the trail is due to the piling up in front of air 

 heated by compression to a state of incandescence. At intervals, 

 sometimes rare, sometimes frequent, but never regular, there are 

 what both the eye and the ear lead us to call explosions, a sudden 

 throwing off of sparks in all directions accompanied by a loud deto- 

 nation. The explanation commonly given of this phenomenon is 

 misleading, if not wholly incorrect, namely, that the breaking of the 

 mass with violent detonation results from the intense heat upon the 

 outside due to the friction, together with the extreme cold of the 

 inner portions, thus causing unequal expansion, and a cleaving away 

 of the outer portion from the inner, thus breaking up the mass. As a 

 theory this may be reasonable, since we see such superficial flakings 

 in intensely heated blocks of granite and other dense rocks. But 

 there are reasons for seeking other explanations of these detonations. 

 As a fact the pieces of aerolites which show fracture in the air have 

 not at all the form of flakes or conchoidal plates. On the contrary 

 they show almost invariably as pieces broken more or less through 

 the middle of a larger mass. This is true of the hundreds of pieces in 

 a meteorite shower, as of Mocs, Pultusk, or Winnebago Co., where 

 the surfaces bearing a secondary crust shov/ clearly the fracture 

 through the middle of the mass. Further, in the case of the Butsura 

 (India) aerolite the several pieces falling one or two miles apart 

 were found to fit together, and the fractures were deep through the 

 mass, not superficial. In short, the explosion theory for meteorite, 

 aerial dismemberment is not sustained by the facts registered on the 

 fragments themselves. 



Our explanation is based on what has been said above of the 

 great compression of the air by the stone passing through it. This 

 compression generates a resistance and a density of air comparable 

 or even superior to that of the stone itself. To this resistance the 

 stone often yields and breaks, as would a stone crowded increasingly 

 against an immovable and impenetrable wall. In the breaking of 

 the meteorite the air in front falls into the vacuum following behind 

 with instantaneous effect, and thus the detonation follows imme- 

 diately on the breaking. In other and probably frequent instances 



