June 13, 1902.] 



SCIENCE. 



947 



University of . America, and describing tlie 

 equipments and instruments of the laboratory 

 of aerodynamics recently erected there by Mr. 

 MattuUath. Both gentlemen have been work- 

 ing on similar problems for many years, and 

 Dr. Zahm was Secretary of the Aeronautical 

 Congress at Chicago in 1893. On the iloor of 

 the laboratory is a wooden tunnel fifty feet 

 long by sis feet square in cross section, having 

 a five-foot suction fan at one end and a net- 

 ting, or two, of close mesh at the other. A 

 wind is thereby generated of practically uni- 

 form velocity and direction, the speed vary- 

 ing less than one per cent., the direction but a 

 small fraction of a degree. In this current 

 are held objects whose resistances, lift, drift, 

 skin-friction, etc., are to be measured. Among 

 the various anemometers and wind-balances 

 designed for this purpose, is a pressure gauge 

 graduated to millionths of an atmosphere, and 

 which may be adjusted to read to less than one 

 ten-millionth. It is connected by hose to one 

 or more Pitot nozzles, and is used to measure 

 the air velocity and pressure at all points of 

 the stream, particularly in the neighborhood of 

 the exposed body. The prime motive of these 

 investigations is to furnish a basis for calcu- 

 lations in aeronautics, particularly in the 

 theory of mechanical flight. 



The Society then adjourned till October 11, 

 1902. 



Charles K. Wead, 



Secretary. 



DISCUSSION AND CORRESPONDENCE. 



VOLCANIC DUST AND SAND PROM ST. VINCENT 

 CAUGHT AT SEA AND THE BARBADOS. 



Some days ago the Weather Bureau for- 

 warded to the Geological Survey for examin- 

 ation a package of volcanic dust which had 

 been collected May 7 at sea on board the 

 British steamship Coya by Capt. Thomas in 

 latitude 11° 21' K, longitude 57° 47' W., or 

 about 275 miles southeast of the island of St. 

 Vincent,' W. I. The dust began to fall about 

 10 p. m. May 7, and Capt. Thomas reports it 

 thickest between midnight and 2 a. m. May 

 8th. At 1 :30 p. m. local or sun time there was 

 absolute darkness. The dust was supposed by 

 Capt. Thomas to have resulted from the erup- 



tion on Martinique or St. Vincent. The upper 

 currents of that region during May 5, 6 and 

 7 were reported west with easterly surface 

 winds. The transfer of the dust is there- 

 fore probably due wholly to upper currents, 

 but the matter cannot be advantageously con- 

 sidered until the facts of distribution over the 

 whole field are available. 



The material is yellowish-gray in color, and 

 to the naked eye of remarkably uniform fine- 

 ness, having been thoroughly assorted from the 

 larger fragments in its long flight. The gritty 

 feel suggests that its particles are sharp and 

 angular, and so they are, in strong contrast 

 with the smooth round grains of the wind- 

 blown desert sands which roll upon the sur- 

 face. 



The particles are so small that a microscope 

 must be used for their study and reveals a 

 range in their size from a diameter of .3 mm. 

 down to .001 mm. or less. The largest particles 

 have a sp. gr. of 2.7, with others almost as large 

 having a sp. gr. 3.3. Considering the great 

 distance this dust traveled through the air 

 before falling to the vessel, it is suprising that 

 it sinlss so rapidly in water. Stirred into dis- 

 tilled water and allowed to stand, in five min- 

 utes fifteen per cent, falls to the bottom, in 

 ten minutes fifty-seven per cent., in ninety 

 minutes ninety-seven, and yet this material 

 traveled through the air 275 miles. It must 

 have been hurled up very high and carried 

 away by strong currents. 



The dust is a mixture of crystal fragments 

 and glass and is clearly of volcanic origin. 

 The crystal fragments constitute about sixty 

 per cent, of the whole mass, and embrace 

 feldspar, pyroxene, magnetite and possibly a 

 number of other minerals not readily identi- 

 fied under such conditions. Feldspar is by 

 far the most abundant mineral, occurring fre- 

 quently in cleavage plates some of which show 

 well-defined albite twinning, while others prob- 

 ably parallel to a different cleavage do not. 

 The extinction angles, which rarely rise to 

 twenty degrees, indicate that the feldspar ap- 

 proximates labradorite or bytownite, although 

 there may be some orthoclase present. Many 

 of the feldspar grains are full of included glass 

 and other matter at times arranged in bands 



