THOUGHTS ABOUT KRAKA1OA. 337 



tendency of the winds at these elevations and in these 

 latitudes, the journey of the Krakatoa dust would have 

 taught us. We shall confine our attention for the pre- 

 sent to the chief phenomena, and we begin with the 

 manifestation of these phenomena which were witnessed 

 in the tropics. 



It seems certain that, having attained their lofty eleva- 

 tion, the mighty clouds of dust were seized by easterly 

 winds, and were swept along with a velocity which may 

 not improbably be normal at a height of twenty miles 

 above the earth's surface. It has been demonstrated by 

 Dr. Vettin, at Berlin, that the upper cirrus clouds in 

 winter at a height of only four or five miles have an aver- 

 age velocity of 44*5 miles an hour. The Rev. W. Clement 

 Ley has shown that the velocities of the upper cirrus 

 clouds often amount to 120 miles an hour. These facts 

 enable us without hesitation to attribute velocities to the 

 great clouds of Krakatoa dust which shall be quite suffi- 

 cient to account for the various phenomena. 



It appears that this cloud of dust started immediately 

 from Krakatoa for a series of voyages round the world. 

 The highway which it at first pursued may, for our pre- 

 sent purpose, be sufficiently defined by the Tropic of 

 Cancer and the Tropic of Capricorn, though it hardly 

 approached these margins at first. Westward the dust 

 of Krakatoa takes its way. In three days it had crossed 

 the Indian Ocean and was rapidly flying over the heart of 

 Equatorial Africa ; for another couple of days it was 

 making a transatlantic journey ; and then it might be 

 found, for still a couple of days more, over the forests of 

 Brazil ere it commenced the great Pacific voyage, which 



