187 



SCIENTIFIC SIDE-LIGHTS 



Dualism 

 Dust 



glass jar, and the heavier particles are per- 

 mitted to subside, the liquid column, when 

 viewed against a dark background, has a de- 

 cidedly bluish tinge. The exceptional blue- 

 ness of the Lake of Geneva, which is fed 

 with glacier-water, may be due, in part, to 

 particles small enough to remain suspended 

 long after their larger and heavier com- 

 panions have sunk to the bottom of the lake. 

 TYNDALL Fragments of Science, vol. i, ch. 

 5, p. 137. (A., 1897.) 



917. DUST OF THE AIR PROVED 

 TO BE ORGANIC Germs in the Air a Cause 

 of Disease. It was Tyndall who first laid 

 down the general principles upon which our 

 knowledge of organisms in the air is based. 

 That the dust in the air was mainly organic 

 matter, living or dead, was a comparatively 

 new truth; that epidemic disease was not 

 due to " bad air " and " foul drains," but to 

 germs conveyed in the air, was a prophecy 

 as daring as it was correct. From these and 

 other like investigations it came to be recog- 

 nized that putrefaction begins as soon as 

 bacteria gain an entrance to the putrefiable 

 substance, that it progresses in direct pro- 

 portion to the multiplication of bacteria, 

 and that it is retarded when they diminish 

 or lose vitality. NEWMAN Bacteria, ch. 3, 

 p. 101. (G. P. P., 1899.) 



918. DUST ON HIGHEST MOUN- 

 TAINS Granular Snow or Neve. The neVe" 

 is composed of stratified granular snow 

 which is white or grayish white in color. 

 The snow on high mountains is apt to be ex- 

 ceedingly fine, light, and dry when first 

 formed ; but by partial melting and refreez- 

 ing it acquires a coarse, granular texture, 

 much like compacted hail, and also becomes 

 consolidated and hard. The surface of the 

 neve is many times so softened by the 

 warmth between summer storms that a thin 

 crust of ice is formed when the temperature 

 is again lowered. This crust is buried be- 

 neath the next succeeding snowfall and re- 

 mains in the growing deposit as a thin 

 stratum of ice. Neves are almost entirely 

 free from stones or dirt, altho even on the 

 highest mountains the dust borne from 

 naked cliffs is widely spread over their sur- 

 faces and diminishes their brilliancy. This 

 general dust-covering is frequently not no- 

 ticeable until some really clean snow sur- 

 face is brought in contrast with it. When a 

 lake on the ne"ve" is drained and leaves a 

 fresh surface of dazzling whiteness, the sur- 

 rounding area frequently shows a gray tint 

 by contrast, thus revealing the presence of 

 dust which has been sprinkled over it. 

 Sometimes the covering of dust, especially 

 on the lower portions of the nave's of Alpine 

 glaciers, is sufficiently pronounced to form 

 a definite division plane when buried by 

 subsequent snowfalls. Illustrations of such 

 an occurrence may frequently be seen in the 

 walls of fissures. RUSSELL Glaciers of 

 North America, int., p. 4. (G. & Co., 1897.) 



919. DUST ON THE HIGH SEAS 

 Volcanic Products Carried Afar. The very 

 finely divided volcanic dust is often borne 

 to enormous distances from the volcano out 

 of which it has been ejected. The force of 

 the steam-current carrying the fragments 

 into the atmosphere is often so great that 

 they rise to the height of several miles 

 above the mountain. Here they may actu- 

 ally pass into the upper currents of the 

 atmosphere and be borne away to the dis- 

 tance of many hundreds or thousands of 

 miles. Hence it is not an unusual circum- 

 stance for vessels at sea to encounter at 

 great distances from land falling showers of 

 this finely divided, volcanic dust. JUDD 

 Volcanoes, ch. 4, p. 71. (A., 1899.) 



920. DUST, VOLGA'S 1C Carried 



Round the World Skies Long Reddened by 

 Reflection Eruption of Krakatau. A re- 

 markable confirmation of this theory was 

 given during the two or three years after 

 the great eruption of Krakatau, near Java. 

 The volcanic debris was shot up from the 

 crater many miles high, and the heavier 

 portion of it fell upon the sea for several 

 hundred miles around, and was found to be 

 mainly composed of very thin flakes of vol- 

 canic 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 continually 

 flowing northward and southward above the 

 equatorial zone; and as these currents 

 reach the temperate zone where the surface 

 rotation of the earth is less rapid they con- 

 tinually flow eastward, and the fine dust 

 was thus carried at a great altitude com- 

 pletely 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 vis- 

 ible sky. These glows continued in dimin- 

 ishing 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 traveled three times round the globe. 

 WALLACE The Wonderful Century, ch. 9, p. 

 77. (D. M. &Co., 1899.) 



921. 



Vast Quantity In- 



calculable Minuteness. Mr. Whymper re- 

 lates that, while standing on the summit of 

 Chimborazo, he witnessed an eruption of 

 Cotopaxi, which is distant more than fifty 

 miles from the former mountain. The fine 

 volcanic dust fell in great quantities around 

 him, and he estimated that no less than two 

 millions of tons must have been ejected 

 during this slight outburst. Professor Bon- 

 ney has examined this volcanic dust from 

 Cotopaxi, and calculates that it would take 

 from 4,000 to 25,000 particles to make up a 

 grain in weight. JUDD Volcanoes, ch. 4, p. 

 69. (A., 1899.) 



