428 Prof. S. P. Langley on the 



the writer, chilled by the cold blast, gave up watching and 

 moved away, leaving the bird still floating about, at the same 

 height in the torrent of air, in nearly the same circle, and 

 with the same aspect of indolent repose. 



If the wind is such a body as it is commonly supposed to 

 be, it is absolutely impossible that this sustention could have 

 taken place in a horizontal current any more than in a calm, 

 and yet that the ability to soar is, in some way, connected with 

 the presence of the wind, became to the writer as certain as 

 any fact of observation could be, and at first the difficulty of 

 reconciling such facts (to him undoubted) with accepted laws 

 of motion seemed quite insuperable. 



Light came to him through one of those accidents which 

 are commonly found to occur when the mind is intent on a 

 particular subject, and looking everywhere for a clue to its 

 solution. 



In 1887, while engaged with the "whirling-table" in the 

 open air at the Allegheny Observatory, he had chosen a quiet 

 afternoon for certain experiments, but in the absence of the 

 entire calm, which is almost never realized, had placed one of 

 the very small and light anemometers made for hospital use 

 in the open air, with the object of determining and allowing 

 for the velocity of what feeble breeze existed. His attention 

 was called to the extreme irregularity of this register, and he 

 assumed at first that the day was more unfavourable than he 

 had supposed. Subsequent observations, however, showed 

 that when the anemometer was sufficiently light and devoid 

 of inertia, the register always showed great irregularity, 

 especially when its movements were noted, not from minute 

 to minute, but from second to second. 



His attention once aroused to these anomalies, he was led 

 to reflect upon their extraordinary importance in a possible 

 mechanical application. He then designed certain special 

 apparatus hereafter described, and made observations with it 

 which showed that " wind " in general was not what it is 

 commonly assumed to be — that is, air put in motion with an 

 approximately uniform velocity in the same strata ; but that, 

 considered in the narrowest practical sections, wind was 

 always not only not approximately uniform, but variable and 

 irregular in its movements beyond anything which had been 

 anticipated, so that it seemed probable that the very smallest 

 part observable could not be treated as approximately homo- 

 geneous, but that even here there was an internal motion to 

 be considered, distinct both from that of the whole body and 

 from its immediate surroundings. It seemed to the writer 

 to follow as a necessary consequence, that there might be a 



