DUST AND SAND STORMS IN THE WEST. 659 



observation, for the quantity of dust settling on floors during 

 such storms is about a fourteenth of an ounce of dust on a sur- 

 face of a square yard in half a day. A maximum estimate made 

 on the basis of the above newspaper accounts would be at least 

 five pounds to a square yard of surface for a storm lasting twenty- 

 four hours. If we then suppose that a house that is twenty-four 

 feet wide and thirty-two feet long has open crevices, which aver- 

 age a sixteenth of an inch in width and have a running length in 

 windows and doors of one hundred and fifty feet, the wind may 

 be supposed to enter half of these crevices with a velocity of five 

 miles per hour for the time the storm lasts, or for twenty-four 

 hours. The dust may be supposed to settle on not less than 

 eighty-five square yards of surface, including floor space and 

 horizontal surfaces of furniture. The minimum estimate, based 

 on these figures, gives us two hundred and twenty-five tons of 

 dust to the cubic mile of air. The maximum estimate would be 

 one hundred and twenty-six thousand tons. 



In the following citations the optical aspects of the dust-laden 

 air are again characterized in a definite way : " The air was so 

 full of sand that it resembled a fog." — " A wind storm struck us, 

 bringing a dense cloud of dust." — " The sky assumed a deep, 

 tawny hue, and fifty yards was the limit of clear vision." — "The 

 dust was so thick and heavy that a person could not see more 

 than a block through it." — " The dust was so thick that it was 

 impossible to see halfway across the street." — " I have seen the 

 dust so fill the air [in a Western dust storm] as to make it diffi- 

 cult to see more than a few rods." — " At times it was impossible 

 to see across the street on account of the flying sand." — " A strong 

 wind was made thick and yellow by flying real estate." — "The 

 wind filled the air with dust as far as the eye could see. It im- 

 mediately became dark, and lamps had to be lighted." — " During 

 the sand storm it was dark as night, and people ran into each 

 other in their flight through the streets." — " The wind was ac- 

 companied by dense clouds of dust that obscured the sky until 

 all was dark as midnight." 



From the phrases used it is evident that the transparency of 

 the atmosphere must have been considerably less than when the 

 sun could be viewed through it, or when objects might be seen 

 dimly at a distance of one or two miles, as in some instances pre- 

 viously mentioned. This difference in the two cases is, of course, 

 due to the increased quantity of dust carried by the air. Such 

 conditions as are described here may readily be produced experi- 

 mentally on a small scale by throwing dust into the air on a 

 windy day. If the quantity of the dust be known, it is necessary 

 only to estimate the degree of opacity produced and the bulk of 

 the air in which the material is dispersed. From a number of 



