Man's physical universe

xanabras

114 THE UNIVERSE A VAST SYSTEM OF PARTS

passed through the Andromid swarm of meteors in

1872 and 1885, it

is estimated that as many as 1000 meteors could be seen at certain

places shooting across the sky at one time. Other showers occur every

August 11, October 20, and December 10. The Leonid showers occur

every 33}4 years, the last one having occurred in 1933. These showers

are probably the result of the passage of the earth through the orbit of

the meteors around the sun, the most brilliant shower occurring when

the earth passes through denser portions of these swarms.

On March 24, 1933, a huge meteor illuminated three of the southwestern

states of the United States with a light more intense than daylight.

In the same year on October 9, one of the most brilliant meteor

showers in history was observed in Europe. It was a result of the

passage of the Giacobini-Zinner Comet near the earth. This comet

was discovered in 1900 and was observed again in 1913, 1926, and in

April, 1933. During this shower it was reported that fully five hundred

meteors per minute were to be seen.

The Larger Meteors Which Reach the Surface of the Earth Are Called

Meteorites.

When someone told President Thomas Jefferson that two Yale

professors had recorded a fall of stones at Weston, Connecticut, he is

said to have remarked, "It is easier to believe that two Yankee professors

will lie than to believe that stones will fall from heaven!"

Some of the meteors are so large that they are not completely burned

up before they reach the earth's surface. These meteors are called

meteorites. It is estimated that an average of one meteorite reaches

the earth's surface per day.

All of the various kinds of meteorites that have been found fall into

three general types: those of metal, called the siderites; those of stone,

called the aerolites; and those which are mixtures of metal and stone,

called siderolites. The siderites are iron alloys which usually contain

from 5 to 20 per cent nickel, and individual specimens are uniform in

composition. They can be differentiated from lumps of metal occurring

on the earth by the unique pattern of crossed lines which show up when

they are etched with acid.

When Joseph Sabene and Sir John Ross visited Greenland in 1818,

they found the Eskimos using tools made from siderites. There are

many historical instances of the use of siderites in making tools, such

as Attila's sword or the arrowheads of certain South American Indians.

The motions of meteorites are usually slowed down by the cushioning

effect of the lower atmosphere. As a result they are cooled by their

less rapid passage through the lower atmosphere.

Meteorites have been

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