Pine Bluff daily graphic., 1894-07-23
nljsT,s PART IN NATURE.
;. rxnrortant Factor in Most Atmospheric z - xohanotnaua.

When a ray of sunlight falls through
 .,,.anerture into a darkened room it is
 -endered visible as far as it extends.
 fvhaf' yve actually see, however, is not
 he ray of light, but the particles of
 gaafino dust rendered visible by it. It might appear, at first glance, that the
 nart played by dust particles in nature
 k of no great scientific or general in-
 ,a,esf. as a matter of fact, however, 4hev play a very important role. Dust k an important factor in almost every .sle enolnenon of the earth's atmosphere.
 In the first place it is due to the dust that the heavens are blue. When we lift auF eyes to the vauIted arch above us we see sllnlight reflected by every particle ~ dust; there is nothing but the dast hetween us and the sun to transmit it's light to us. Light trayerses all gases, no matter what their chemical compo- sition. in straight lines, and is invisi- hle The dust intercepts and reflects it an all sides, and makes the whole at ,oosubere luminous, in the same man. f,er as it makes the track of the suns rays Visible in a darkened room.
 Without dust there would be no blue flrmament; the Heaven would be black er than we sec it on moonless nights. On this black background the glowing sun would shine out sharply, and the same sharp contrast of intense light and deep shadow would characterize inc surface of the earth. There would be nothing to subdue this sharp con twasf but the moon and stars which would remain visible by day The il' lumination of the earth would be similar to that which we ob- serve when looking at the moon through telescopes; for the moon has no atmospheric envelope aud Consequently no dust in suspen- sion. It is due entirely to the dust that i've enjoy our soft, uniformly diff fused daylight, for which our eyes are especially adapted; and it is the dust which contributes so much to the beau tv Of the landscape.
 But, while the foregoing explains how the dust makes the whole vault of heaven light, it does net explain why it is chiefy the blue rays of the white sunlight that are reflected, and, only to small extent, the green yellow and red rays.
 This is dependent of the size of the dust particles. v It is only the finest of them that are borne by the air cur rents into every stratum of air and t is only these fine. widely-diffused dust particles that are of any significance in this connection. Now let us con sider the mechanism of light and the extreme shortness of the ether waves which constitute it's essence. These waves, although all mieroseopically snali, vary considerably in length. The fine Atmospheric dust includes many particles large enough to reflect the short blue ether waves, fewer particles capable of refeeting green and yellow, and still fewer large enou gh to inHu- ence the long red ethereal waves. The red light, conseqently. passes through the great ma jority of the dust particles, colnparatively unhindered, the blue rays. on the contrary. are intercepted and diffused, and so become visible This is the reason that the finest dust
 and so. too the frmament-app blue.
 So. then. the finest dust appears blue You may observe that the wreath that curls upward from the burning end of cigar is blue. while the smoke drawn through and exhaled is whitish The particles in the latter case have united and become large enough to reflect white light. So, too, in the country on q clear day the sky IS blue, but in the city 1t appears whitish, because of the greater number of coarse dust particles in the air It is isespecially on mountain heights that the Sky is so intensely blue, because the rarefied atmosphere supports only the finest dust particles. At great heights the sky would be almost black if tlaere were no dust particles in sus- pension. We see it grow pale as we look at 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, however, the vapor re- falns it's watery character, and does not condense on the floating dust. It is not until the aerial currents have borne it 10 higher and colder regions that it is oondensed to clouds
 This brings us to the most important role played by dust in our atmosphere; It's influence in determining the rain- fall due to the fact that vapor fluid- aiies upon the dust particles.
 It may be accepted as beyond ques- tion that, of all the water evaporated by the sun from the surface of land and sea, not one drop returns winch has not condensed upon particle of dust as a nucleus This is easily demonstrated We ill large flask with air which has been filtered through cotton waddings unfli all the original dust is driven out and the flask is full of dustless air. Into this dustless air turn current of steam from kettle, and you will find and, therefore, invisible. &ot trace of the cloudy appearance we associate with steam. The only thing noticeable is that the inner wall of the nask begin to drip; the vapor condenses neFe as 1t cools, because there is nsthipg else for it to eondense op. But DOW ordinarily dust laden air into the nesk, and the vapor at once assumes sne familiar cloudy appearance due to