432 Prof. S. P. Langley on the 



owing to the weight and inertia of the anemometer, this is far 

 from doing justice to the actual irregularities of the wind, on 

 the other it equally shows that the wind was far from being a 

 body of even approximate uniformity of motion, and that 

 even when considered in quite small sections, the motion was 

 found to be irregular almost beyond conception— certainly 

 beyond anticipation ; for this record is not selected to repre- 

 sent an extraordinary breeze, but the normal movement of an 

 ordinary one. 



By an application of these facts, to be presented later, I 

 then reached by these experiments the conclusion that it was 

 theoretically possible to cause a heavy body wholly immersed 

 in the wind to be driven in the opposite direction, e. g. to 

 move east while the wind was blowing west, without the use 

 of any power other than that which the wind itself furnished, 

 and this even by the use of plane surfaces, and without taking 

 advantage of the more advantageous properties of curved ones. 



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 

 illustrate the essential fact of the rapid and continuous fluctua- 

 tions of even the ordinary and comparatively uniform wind, 

 yet owing to the inertia of the arms and cups, which tended 

 to equalize the rate (the moment of inertia was approximately 

 40,000 gr. cm. 2 ), 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 re- 

 presenting its potential work, were not adequately recorded. 



In January 1893 I resumed these observations at Washing- 

 ton with apparatus with which 1 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 metres) above the ground, and the anemo- 

 meters, which were located above the parapet, being 153 feet 

 (46*7 metres) above the ground. I placed them in charge 

 of Mr. George E. Curtis, with instructions to take observa- 

 tions under the conditions of light, moderate, and high winds. 

 The apparatus used was, first, a Weather Bureau Eobinson 

 anemometer of standard size, with aluminium cups. Diameter 

 to centre 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 



