METEORIC PHENOMENA. 289 



The estimated velocity of tbeso bodies is somewhat more than three hun- 

 dred miles per minute, though one meteor of immense size, which is supposed 

 to have passed within twenty-five miles of the earth, moved at the rate of 

 twelve hundred miles per minute. Owing, however, to the short time the 

 meteor is visible, and its great velocity, accurate observations can not bo 

 made upon it ; and all estimates respecting their distance, size, etc., must be 

 considered as only approximations to the truth. 



--„.., Very many of the meteorites which have fallen at different 



Wnat IS known 



respecting the tunes and m different parts of the globe, resemble each other 



^roUtes?°° °^ ^° closely, that they would seem to have been broken from 

 the same piece or mass of matter. 

 Most of them arc covered with a black shining crust, as if the body had 

 been coated with pitch. "When broken, their color is ash-gray, inclining to 

 black. They consist for the most part of malleable iron and nickel but they 

 often contain small quantities of other substances. They do not resemble in 

 composition any other bodies found upon the surface of the earth, but have a 

 character of their own so peculiar that it enables us to decide upon the me- 

 teoric origin of masses of iron which are occasionally fotand scattered up and 

 down the surface of the earth, as in the south of Africa, in Mexico, Siberia, 

 and on the route overland to California. Some of these masses are of immense 

 weight, and ixndoubtedly fell from the atmosphere. 



■What is the ^^^- Four hvpotheses have been advanced 

 Bupposedon^n j.^ account foF the origin of these extraordinary- 

 bodies ? bodies : 1, That they are thrown up from ter- 

 restrial volcanoes ; 2. That they are produced in the at- 

 mosphere from vapors and gases exhaled from the earth; 

 3. That they are thrown from lunar volcanoes ; 4. That 

 they are of the same nature as the planets, either derived 

 from them, or existing independently. 



The fourth of these suppositions most fully explains the facts connected 

 with the appearance of meteorites, and the third Ukewise has some strong 

 evidence in its favor. 



Hovr do shoot- ^^"^^ Shooting-stars differ in many respects 

 ftom m"t4'r^'? from mctcors. Their altitude and velocity are 

 greater ; they are far more numerous and fre- 

 quent, and are unaccompanied by any sound or explosion. 

 Their brilliancy is also much inferior to that of the me- 

 teor, and no portion of their substance is ever known to 

 have reached the earth. 



At what height The altitude of shooting-stars is supposed to vary from sfx 

 do shooting- to four hundred and sixty miles, the greatest number appear- 

 •turs appear . ing at a height of about seventy miles. Owing to their num- 



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