376 THE POPULAR SCIENCE MONTHLY. 



of the observer. A single explosion is rare. There are generally two 

 or three of them. Sometimes they are violent enough to shake houses 

 and give the impression of an earthquake, as was the case in Iowa 

 when the meteor of the 12th of February, 1875, fell. They are often 

 heard over a considerable extent of country, as was the case with the 

 Orgueil meteors, the explosions of which were heard three hundred 

 miles away. When we reflect that these detonations take place at 

 heights where the thinly rarefied air affords a very poor medium for 

 the propagation of sound, we become satisfied that they must be 

 extremely violent. Sometimes a trail of vapors is perceived in the 

 regions of the atmosphere which the body has traversed. These phe- 

 nomena are manifested in the most diverse regions of the globe, at 

 every season and every hour, and frequently in calm and cloudless 

 weather. Storms and whirlwinds, therefore, have nothing to do with 

 them. Their speed as observed by us being only relative, varies ac- 

 cording to the correspondence or non-correspondence of the direction 

 of their path with the course which the earth is pursuing. 



The outer configuration of meteorites is remarkable for its frag- 

 mentary aspect, or for its angular formations and its likeness to irregu- 

 lar polyhedrons, the edges of which have been blunted. 



The number of stones brought down in a single meteoric shower is 

 extremely variable. Sometimes only one is found ; sometimes many ; 

 and, in rare cases, hundreds and thousands. At the instant the stones 

 reach us their velocity is small, compared with that which the body of 

 which they are fragments had previous to the explosion. If they are 

 of considerable size, they will perhaps bury themselves at a slight 

 depth under a yielding soil, and remain there unperceived. After all 

 the light they give and the noise they make in their flight, the minute- 

 ness of the masses which we find upon the surface of the ground is 

 sometimes surprising. The largest one ever found at St. Catherine, 

 Brazil, 1875 weighed 25,000 kilogrammes ; stones of more than 300 

 kilogrammes, like the one that fell at New Concord on the 1st of May, 

 1860, are rare, while the weight of 50 kilogrammes is seldom exceeded. 

 Often whole meteorites weigh only a few grammes, or are of the size 

 of a hen's egg, a walnut, or a hazel-nut ; and masses of still smaller 

 ones have been observed when they fell upon a bed of snow, as at 

 Hersle, near Upsala, Sweden, in 1869, when many of the stones weighed 

 only a few decigrammes, and one of them as little as six centigrammes. 

 These little grains, it should be remarked, were not fragments broken 

 off by the shock of larger pieces against the ground ; but each one 

 was a complete meteorite, enveloped in a crust of half-melted matter. 

 That so small meteors had not been noticed before is explained by the 

 difficulty of distinguishing them from the particles composing the gen- 

 eral surface, among which they are lost. 



When the meteors of the same shower are numerous, they are gen- 

 erally distributed at various points within an elongated oval area, the 



