196 ROCHESTER ACADEMY OF SCIENCE. 



ness of form. Very soft is the extremely attenuated air into the 

 upper layer of which a meteorite plunges in its downward flight, 

 as it leaves the realms of outer space; but after the first fraction 

 of a second the mass is opposed by great density of the air through 

 which it cleaves its way only by its momentum and with ever in- 

 creasing friction. No longer is the mass passing through a gas, for 

 its flight has changed the air by compression into a virtually solid 

 substance. The enormous pressure exerted upon a flying body by 

 its compression of the air through which it passes has been estimated 

 by physicists. They tell us that a body traveling 20 miles a second 

 through the lower atmosphere would have upon it a pressure of 'jy 

 cwt. per square inch. Reichenbach, Jr., has shown that the air 

 crowded in front of a meteorite with a velocity of 40 miles per 

 second would have, by reason of its compression, a heat of over 

 7000 degrees Fahrenheit — a heat calculated to melt away any sur- 

 face which it enveloped. It is to the melting, rubbing and chiselling 

 effect of this air compression that we may attribute all the glazing, 

 pitting, hollowing and channelling which we find on the front an.l 

 sides of meteorites. As may be expected, the iron meteorites have 

 been less rapidly eroded than the stones. They, too, are apt to be 

 in large pieces. Only iron would withstand such a pressure, stone-5 

 breaking with the tension. The extent of this erosion will depend 

 nuich upon the composition of the stone, also upon its form. Th.e 

 worn-oflf particles fly off, making at the same time great streams of 

 sparks. Probably by far the larger number of the masses are en- 

 tirely worn away. The wonder is that an)- part of the stone re- 

 mains. 



It is probable that the external combustion of a meteorite ceases 

 before it wholly loses its cosmic impulse; its incandescence and 

 luminosity ceasing also. This great heat is confined to the exterior 

 of the mass from which the melted particles are instantly brushed 

 away as they form. It thus results that the fiery, flaming mass is 

 in fact mainly cold. It brings with it the temperature of the celes- 

 tial spaces, which has been estimated at 504 degrees (Fahrenheit) 

 below zero. The aerolite Dhurmsala in India, Pegu in Burmah, 

 and Lissa in Bohemia were thus cold when they reached the earth. 

 In the Pultusk meteorite shower which fell during a snowstorm in 

 January, 1868, one of the stones weighing four pounds was found 

 covered with light snow ten minutes after the fall. Orgueil, al- 



