2 THE IXTEKNAI. WOKK OF THE WIND. 



sometimes for at least a considerable fraction of an hour. It is frequently sug- 

 n,| by those who know these facts only from books, that there must be some 

 quivering of the w ings, so rapid as to escape observation. Those who do know them 

 from observation, are aware that it is absolutely certain that nothing of the kind 

 takes place, and that the birds sustain themselves on pinions which are quite 

 rigid and motionless, except for a rocking or balancing movement involving 

 little energy. 



The writer desires to acknowledge his indebtedness to that most conscientious 

 observer, M. Mouillard,* who has described these actions of the soaring birds with 

 incomparable vividness and minuteness, and who asserts that they, under certain 

 circumstances, without flapping their wings, rise and actually advance against 

 the wind. 



To the writer, who has himself been attracted from his earliest years to the 

 mystery which has surrounded this action of the soaring bird, it has been a subject 

 of continual surprise that it has attracted so little attention from physicists. That 

 nearly inert bodies, weighing from 5 to 10, and even more, pounds, and many hun- 

 dred times denser than the air, should be visibly suspended in it above our heads, 

 sometimes for hours at a time, and without falling, — this, it might seem, is, without 

 misuse of language, to be called a physical miracle ; and yet, the fact that those 

 whose province it is to investigate nature, have hitherto seldom thought it deserving 

 attention, is perhaps the greater wonder. 



This indifference may be in some measure explained by the fact that the 

 largest and best soarers are of the vulture kind, and that their most striking evolu- 

 tion- are not to be seen in those regions of the Northern Temperate Zone where 

 the majority of those whose training fits them to study the subject are found. 

 Even in Washington, however, where the writer at present resides, scores of great 

 birds may be seen at times in the air together, gliding with and against the wind, 

 and ascending higher at pleasure, on nearly motionless wings. "Those who have 

 not seen it," says M. Mouillard, " when they are told of this ascension without the 

 expenditure of energy, are always ready to say, 'but there must have been move- 

 ments, though you did not see them,'"; "and in fact," he adds, " the casual witness 

 of a single instance himself, on reflection, feels almost a, doubt as to the evidence 

 of his sense-, when the) testify to things so extraordinary." 



Quite agreeing with this, the writer will not attempt any general description 

 of his own observations, but as an illustration of what can sometimes be seen, will 

 give a single one, to whose exactness he can personally witness. The common 



*L. P. Mouillard, L' Empire de T Air, Paris : G. Masson. 



