Fitsion-Structurex in Meteor Hes. 2iJi) 



on increasing with the square of the velocity. The average 

 velocity of a number of well-observed aerolites* may be taken 

 at 34 — 39 miles per second, and so, it will be readily seen, a very 

 high temperature Avould be attained. 



The heat thus generated is of course sufficiently intense to 

 fuse any substance known ; but it must be remembered that this 

 heat is gradually acquired, and acquired from without to within; 

 and moreover, the body is not exposed for any great length of 

 time to this high temperature ; hence it will naturally follow, 

 that if this temiDorary heating is to exert any permanent effect, 

 it will be the exterior of the body that will suffer the change. 



And so it proves to be. Examination of a number of aero- 

 lites reveals the fact that they are covered with a black crust or 

 rind, which crust is the result of fusion. This crust, however, 

 is generally very thin. 



To examine into this, I had prepared three sections of the 

 meteorite which fell at Aigle, France, April 26th, 1803 (Me- 

 teorite 8, Slides 13, 14, 15). This specimen was of a dark 

 grey color, with one face or side covered with the black fusion- 

 crust. 



The first section was cut from the crust only ; the second was 

 prepared from the inner, unaltered portion; while the third was 

 cut from across both crust and unchanged part. 



The appearance that these three sections present under the 

 microscope is shown on Plate XX, Figs. 7, 8, 9. Examined 

 with 300 D. power, the first (Slide No. 13) exhibits a highly 

 crystalline structure. The crystals are apparently thrown 

 "criss-cross," the one over the other; generally they are 

 grouped so as to leave in their midst a circular opening which 

 has once been filled by metal, — i. e., they have probably crystal- 

 lized around some small globule of metal as a nucleus. In 

 most cases, this has been lost in the cutting of the section ; 

 in a few instances, however, it remains. This section polarizes 

 beautifully. 



The second slide (No. 14) shows a sort of fibrous structure, 

 entirely different from the preceding, as will be seen from Plate 



Phipson : Meteors, Aerolites and Falling Stars. 



