TRANSACTIONS OF THE SECTIONS. 



17 



But the pressure of the atmosphere is equal to 32 feet of -water, of the -weight of 

 49-71 lbs. avoirdupois ; for 1 cubic foot is equal to 1590-7 lbs., or 42 times the 

 pressure on one square foot of a destructive hun-icane. From other data I infen-ed 

 the pressure 55 times the pressure of a devastating hurricane. Evidently these 

 nimibers are all approximations. It may be observed here, that it is this pressure 

 of the atmosphere -which enables it to remain in its imdisturbed state, while the 

 rate of movement of a point in the equator, by rotation, is no less than 1340 feet 

 in one second of time. 



When a fragment of rock enters the atmosphere -with the great velocity above 

 mentioned, the particles of air, though remote ii-om each other at the height where 

 the fragment moves, and at the low temperature of cosmic space (some 100° 

 Centigr. below the freezing-point of water), -wUl be canied along forcibly, without 

 the possibility of giving way or flo-wing oft laterally, the rapidity of motion being 

 too excessive. The air -will unavoidably be compressed, and both heat, electricity, 

 and light must be developed. A centre of expansion must be generated exactly 

 in front of and close to the moving fragment, and the compressed air, heated to 

 whiteness, wUl be forced out on all sides perpendicularly to the direction of the 

 track of the meteor. But as the latter still advances, the pi-essure of the opposino- 

 atmosphere upon the white-hot shining disc -will round it off, so as to prodnce the 

 oval fireball as it appears to our eye. 



I beg leave to refer to the diagram, fig. 2 — ^the meteor moving from A to B, the 



Fig. 2. 



centre of expansion forming at C, the white-hot air being forced outperpendicularly 

 in the direction of DD, and rounded ofi' again in its coiu-se at Ei^ to meet at A, 

 enclosing of course a perfect vacuum. Now, on the earth's surface one square foot 

 of " destructive hurricane " -will produce a pressiu-e of 37-9 lbs., while it travels at 

 the rate of 134-9 feet in one second of time. One square foot of a meteor supposed 

 to travel at the rate of 35 nuks, or of 35 times 5280 feet, in the same second of time 

 (a distance 1370 times greater than the former), may be considered to exert a 

 pressiu-e of 61,923 lbs., or of more than thirty-two atmospheres. These amazing, 

 though of course only approximate, numbers will certainly give sufficient cause for 

 an increase in the temperatui-e and development of light. This construction, I be- 

 lieve, -will not be considered inconsistent with observations, or contradictory to 

 weU-known physical facts. It accounts in particular for the fact that from fii-eballa 

 of very considerable magnitude, stony or iron specimens are obtained of very dimi- 

 nutive size and weight. The heat evolved by compression is sufficient to melt the 

 surface. From some peculiarities -visible on the siuface of aerolites — the well- 

 1861. 2 



