86 



NATUEAL SCIENCE NEWS. 



the size of the dust particles. It 

 is only the finest of them that are 

 borne by the air currents into every 

 stratum of air, and it only these 

 fine, widely diffused dust particles 

 that are of any significance in this 

 connection. Now, let us 'consider 

 the mechanism of light and the ex- 

 treme shortness of the ether waves 

 which constitute its essence. These 

 waves, although all microscopically 

 small, vary considerably in length. 

 The fine atmospheric dust includes 

 many particles large enough to re- 

 flect the short blue ether waves, 

 fewer particles capable of reflect- 

 ing green and yellow, and still few- 

 er large enough to influence the 

 long red ethereal waves. The red 

 light, consequently, passes through 

 the great majority of the dust par- 

 ticles comparatively unhindered; 

 the blue rays on the contrary, are 

 intercepted and diffused, and so be- 

 come visible. This is the reason 

 that the finest dust — and so, too, 

 the firmament — appears blue. 



So, then, the finest dust appears 

 blue. You may observe that the 

 wreath that curls upward from the 

 burning end of a cigar is blue, 

 while the smoke drawn through 

 and exhaled is whitish. The par- 

 ticles in the latter case have united 

 and become large enough to re- 

 flect white light. So, too, in the 

 county, on a clear day, the sky is 

 blue; but in the city it appears 

 whitish, because of the greater 

 number of coarse dust particles in 

 the air. It is especially on moun- 

 tain heights that the sky is so in- 

 tensely blue, because the rarefied 

 atmosphere supports only the fin- 

 est dust particles. At great 

 height the sky would be almost 

 black, if there were no dust parti- 

 cles in suspension. We see it 

 grow pale as we turn our eyes to 

 the lower strata of air toward the 

 horizon. But why is the sky in 

 Italy and in the tropics so much 

 deeper blue than with us? Is the 

 dust finer there? As a fact, it 

 really is. Not that finer dust rises 

 there; but in our climate the dust 

 particles are soon saturated with 

 water vapor, which makes them 

 coarser. In warmer regions, how- 

 ever, the vapor retains its watery 

 character and does not condense 

 on the floating dust. It is not un- 

 til the aerial currents have borne it 

 to higher and colder regions that it 

 is condensed to clouds. 



This brings us to the most im- 

 portant role p'ayed by dust in our 

 atmosphere: its influence in deter- 

 mining rainfall, due to the fact 

 that vapor fluidifies upon the dust 

 particles. It may be accepted as 



beyond question that of all the 

 water evaporated by the sun from 

 the surface of land and sea, not 

 one drop returns which has not 

 condensed upon a particle of dust 

 as a nucleus. This is easily de- 

 monstrated. We fill a large flask 

 with air which has been filtered 

 through cotton waddings until all 

 the original dust is driven out and 

 the flask is full of dustless air. In- 

 to this dustless air turn a current 

 of steam from a kettle and you will 

 find it transparent, and, therefore, 

 invisible. Not a trace of the cloudy 

 appearance we associate with 

 steam. The only thing noticeable 

 is that the inner walls of Ithe flask 

 begin to drip; the vapor condenses 

 here as it cools, because there is 

 nothing else for it to condense on. 

 But blow ordinary dust-laden air 

 into the flask and the vapor at 

 once assumes the familiar cloudy 

 appearance due to its condensa- 

 tion on the dust particles and 

 it begins to rain in the flask. The 

 reason for this is that the vapor 

 condenses on the dust particles 

 and freights them until the}' sink 

 as rain drops. 



Without dust, then, we would 

 have no fog, no clouds, no rain, 

 no snow, no brilliant hued sunsets, 

 no cerulean sky. The surface of 

 the earth itself, the trees, the 

 houses, along with man and beast, 

 would be the onlyoobjects on which 

 the vapor could condense, and 

 these would begin to drip when- 

 ever the air was cooled sufficiently. 

 In winter everything would be cov- 

 ered with a crust of ice. Our 

 clothes would become saturated 

 with water condensing upon them. 

 Umbrellas would be of no avail. 

 The vapor-laden atmosphere, more- 

 over, would penetrate to our rooms 

 and condense upon the walls and 

 furniture. In short, the world we 

 live in would be quite another 

 world if there were no dust. Since 

 scientists began to realize the im- 

 portant part played by dust in the 

 economy of nature, measures have 

 been taken to count the particles 

 in a given space. In London and 

 in Paris at the surface a cubic cen- 

 timeter has been found to contain 

 nearly a quarter of a million parti- 

 cles. On the top of the Eiffel 

 Tower there are about half as 

 many, while in the high Alps there 

 are only about two hundred parti- 

 cles to the centimeter. A great 

 deal of the dust at high altitudes is 

 comic dust, consisting like the me- 

 teorites, of carbon and iron. — Die 

 Gartenlaube {Leipzig). 



Spain's Big Meteorite. 



In our issue of February 22 we 

 called attention to the bursting of 

 a great aerolite over Madrid on 

 February 10. The Spanish news- 

 papers have now reached this 

 country and give full details of the 

 event. This phenomenon is sel- 

 dom observed on so startling a 

 scale. The sky was cloudless, the 

 streets were just beginning to be 

 thronged with traffic and pedes- 

 trians, when the deafening sound 

 of the explosion was heard. Those 

 who happened to be looking at the 

 sky say that the instant of the ex- 

 plosion there was a vivid glare of 

 blinding light and then there in- 

 stantly appeared at the place 

 where the disturbance originated 

 what looked like a cloud of white 

 and bluish tint, bordered with red, 

 which moved east at a tremendous 

 rate, leaving behind a thin train il- 

 lumined by the sun that may have 

 been dust particles. The whole 

 city appeared to be shaken as if by 

 an earthquake, and the agitation 

 of the atmosphere was shown by 

 the rapid fall and rise of the bar- 

 ometer. The terror inspired by 

 the occurrence was very great, par- 

 ticularly among the ignorant and 

 superstitious. Many people did 

 not recognize the origin of the 

 phenomenon and thought some 

 terrible catastrophe had occurred. 

 The energy of the disturbance prob- 

 ably equaled that of the explosion 

 of a large powder magazine. Many 

 windows were shattered and walls 

 injured, but fortunately no one was 

 killed. The aerolite was visible 

 over at least three-fourths of Spain 

 as it shot through the air above 

 the peninsula. Some damage was 

 done at places along its route, for 

 the great meteorite partly disinte- 

 grated on its way, and the incan- 

 descent fragments that showered 

 npon the town of Lograno set two 

 buildings on fire, and at Burgos 

 three free fragmeuts fell among the 

 houses. Other pieces of the stone 

 that were fluug off near Madrid 

 were picked up while still hot. — 

 Scientific American. 



A large collection of 17,000 stuff- 

 ed birds and many series of bird 

 skeletons has been bequeathed 

 to the British Museum by the 

 late Mr. Henry Seebohm, the nat- 

 uralist. It is the mosti valuable 

 gift made to the natural history 

 section of the museum in a quarter 

 of a century. Its ornithological 

 collection is now the largest in the 

 world, consisting of 300,000 speci- 

 mens. — Scientific American. 



