B. TERRESTRIAL PHYSICS AND METEOROLOGY. 105 



well known, the only direct means of observing the direction 

 of motion of the upper currents of air. These meteors be- 

 come visible when they are at an altitude of about seventy 

 miles above the earth's surface, and they disappear, general- 

 ly, at a height of about forty miles and upward. They be- 

 come luminous only because of the resistance of the air 

 through which they are passing, with an average velocity of 

 twenty-five miles per second. One of these bodies sometimes 

 leaves behind it a train of luminous matter, Avhich remains 

 visible often only a fraction of a second, but sometimes for 

 minutes ; and, in rare cases, for nearly or quite an hour. This 

 train appears in the day-time as a smoky cloud ; in the night- 

 time as a bright track. During the first few seconds after it 

 has been formed it looks like a straight line along the track 

 that has been passed over by the meteor; but instantly it 

 begins to broaden, and usually the ends fade out first. In a 

 few seconds more, it is seen to become crooked, and it as- 

 sumes somewhat the shape of a letter S. The height of these 

 trains averages about fifty miles, and they are usually not 

 more than five or ten miles lono-. After the ends of the train 

 have faded away, the central portion still remains, having by 

 that time generally assumed the shape of a small round 

 cloud, which drifts slowly away. Professor Newton has ob- 

 served this drifting very accurately. He states that such 

 clouds as he has watched had apparently a velocity of about 

 one mile a minute ; but that he has not been able to detect 

 any law governing the direction of this drifting. It does 

 not appear to have a uniform direction. It is quite as like- 

 ly to move to the north as to the south, to the east as to the 

 west. In fact, he records that, during the same evening, the 

 different trains that he has observed will drift in diflferent di- 

 rections, and he thinks it most reasonable to conclude that 

 in the highest regions of the atmosphere there is a complex 

 system of currents and winds, precisely similar to that which 

 exists at the earth's surface. 



THE TYPHOOXS OF CHIXA AXD JAPAX. 



The importance to navigators of a clear perception of the 

 laws of storms is apparent from a consideration of the ex- 

 perience of the captain of the ship Argyleshire during the 

 typhoon of the 11th of September, 1872, in the Japan Sea. 



E 2 - 



