THE IMPORTANCE OF DUST. 75 



play of gorgeous ever-changing tints occurs which are 

 at once the delight of the beholder and the despair of the 

 artist. And all this unsurpassable glory we owe to 

 dust! 



A remarkable confirmation of this theory was given 

 during the two or three years after the great eruption of 

 Krakatoa, near Java. The volcanic debris was shot up 

 from the crater many miles high, and the heavier por- 

 tion of it fell upon the sea for several hundred miles 

 around, and was found to be mainly composed of very 

 thin flakes of volcanic glass. Much of this was of 

 course ground to impalpable dust by the violence of the 

 discharge, and was carried up to a height of many miles. 

 Here it was caught by the return current of air con- 

 tinually flowing northward and southward above the 

 equatorial zone; and as these currents reach the temper- 

 ate zone where the surface rotation of the earth is less 

 rapid they continually flow eastward, and the fine dust 

 was thus carried at a great altitude completely round the 

 earth. Its effects were traced some months after the 

 eruption in the appearance of brilliant sunset glows of an 

 exceptional character, often flushing with crimson the 

 whole western half of the visible sky. These glows 

 continued in diminishing splendor for about three years, 

 they were seen all over the temperate zone, and it was 

 calculated that, before they finally disappeared, some of 

 this fine dust must have travelled three times round the 

 globe. 



The same principle is thought to explain the exquisite 

 blue color of the deep seas and oceans and of many 

 lakes and springs. Absolutely pure water, like pure 

 air, is colorless, but all seas and lakes, however clear and 



