4S 8. P. Langley — Internal Work of the Wind. 



This power. I further already believed myself warranted by 

 these experiments in saying, could be obtained by the move- 

 ments of the air in the horizontal plane alone, even without 

 the utilization of currents having an upward trend. But I 

 was obliged to turn to other occupations, and did not resume 

 these interesting observations until the year 1893. 



Although the anemometer used at Allegheny served to illus- 

 trate the essential fact of the rapid and continuous fluctuations 

 of even the ordinary and comparatively uniform wind, yet ow- 

 ing to the inertia of the arms and cups, which tended to equalize 

 the rate (the moment of inertia was approximately 40,000 

 gr cm 1 ) and to the fact that the record was only made at every 

 twenty-fifth revolution, the internal changes in the horizontal 

 component of the wind's motion, thus representing its poten- 

 tial work, were not adequately recorded. 



In January, 1893, I resumed these observations at Washing- 

 ton with apparatus with which I sought to remedy these 

 defects, using as a station the roof of the north tower of the 

 Smithsonian Institution building, the top of the parapet being 

 142 feet (43'3 meters) above the ground, and the anemometers, 

 which were located above the parapet being 153 feet (46*7 

 meters) above the ground. I placed them in charge of Mr. 

 George E. Curtis, with instructions to take observations under 

 the conditions of light, moderate and high winds. The appa- 

 ratus used was, first, a Weather Bureau Robinson anemometer 

 of standard size, with aluminum cups. Diameter, to center of 

 cups 34 cm ; diameter of cups 10*16 cm ; weight of arms and cups 

 241 grams ; approximate moment of inertia 40,710 gr. cm 2 . 



A second instrument was a very light anemometer, having 

 paper cups, of standard pattern and diameter, the weight of 

 arms and cups being onlv 74 grams, and its moment of inertia 

 8,604 gr. cm 2 . 



With this instrument, a number of observations were taken, 

 when it was lost by being blown away in a gale. It was suc- 

 ceeded in its use by one of my own construction, which was 

 considerably lighter. This was also blown away. I afterward 

 employed one of the same size as the standard pattern, weigh- 

 ing 48 grams, having a moment of inertia of 11,940 gr. cm 2 , 

 and finally, I constructed one of one-half the diameter of the 

 standard pattern, employing cones instead of hemispheres, 

 weighing 5 grams, and having a moment of inertia of but 

 300 gr. cm 2 . 



In the especially light instruments, the electric record was 

 made at every half revolution, on an ordinary astronomical 

 chronograph, placed upon the floor of the tower, connected 

 with the anemometer by an electric circuit. Observations 



