44 S. P. Langley — Internal Work of the Wind. 



taken place in a horizontal current an} 7 more than in a calm, 

 and jet 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 unfavorable 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, espe- 

 cially 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 practicable 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 

 potentiality of what may be called " internal work "* in the 

 wind. 



* Since the term " internal work " is o/ten used in thermodynamics to signify 

 molecular action, it may be well to observe that it here refers not to molecular 

 movements, but to pulsations of sensible magnitude, always existing in the wind, 

 as will be shown later, and whose extent and extraordinary possible mechanical 

 importance it is the object of this research to illustrate. The term is so signifi- 

 cant of the author's meaning, that he permits himself the use of it here, in spite 

 of the possible ambiguity. 



