THK EAiriHE OF THK AIK'. 451' 



and tliat the y-uidance is rlic result of skilUiil iiunidnivers; so that by 

 a iiiodcrato wind a man can, with an ai'iophmc, un})r()vided with any 

 motor whatever, rise ui> into the air and direct himself at will, even 

 against the wind itself, ^fa-n therefore can, witii a rigid surface and 

 a [)roperly designed a])paratus, repeat the niaineuvers of ascension 

 and guidance performed by the soaring- birds, and Avill need to ex])en(l 

 no muscular force whatever, save for guidance. 



As to the exaet shape to l)e given to the ai'roplane. it need not be 

 discussed in this chapter, because there are many shapes an<l devices 

 which may be e!n[>loyed; but all forms of apparatus, however dissimi- 

 lar, must be based ufjon this idea, Avhich 1 repeat: ^Vsceusion is the 

 result of the skillful use of the ])ower of the wind, ami no other force 

 is required. 



It will doubtless be very difficult ibi' many i>ers(ins to admit that a, 

 bird can, with a moderate wind, remain a whole day in the aii' with no 

 expenditure of force. They will endeavor to sup{)ose some indiscern- 

 ible pressures or souie imperceptible l)eats. In i)oint of fact the hu- 

 man mind does not readily admit the above attirmation; it is astonished 

 and seeks for all the evasions it can tind. xill those who have not seen 

 the performance say, when ascension without expenditure of force is 

 mentioned to them. ''Oh, well, there were some motions which escaped 

 your observation." It even occurs sometimes that a chance or super- 

 ficial observer who has had the good fortune to see this nunneuver 

 well performed by a bird, when he tuins it over in his mind after- 

 wards feels a doubt invading his understanding; the i)erformance 

 seems so astonishing, so paradoxical, that he asks himself whether his 

 eyes did not deceive him. 



Foi' observation of this manu'uver, in (nder to carry absoluti' con- 

 viction, must bear ui)on the performance of the largest vultures, and 

 ni»ou them alone, and this is the reason : it is because all the other birds 

 which ascend into the air by this process do not i)erform the necessary 

 decomposition of forces required in all its naked simplicity. 



if w(; observe small birds, we see (;reatures weighing only a lew 

 ou)u^es, the martin, the bee-eater, etc., i)erform this nmnoniver in high 

 winds and high, up in llui air. But even when carefully obseived with 

 ate]esco]>e n doubt reniains, in conseiiuence of the enormous ]»(»wer of 

 the mai'iin. wito can jn'o'ect himself forward more than a yard with a 

 single beat of Ming. 



Th(? kites, buzzards, bustards, etc., when they rise, wheeling round, 

 j)erlbrni such ci)iuplieate(l manoMivers as to permit a doubt. - - - 

 To reach a vigorous, undeniable demonstration, we must discard even 

 the great eagle, Avhose nnino'uver is not easily followed by the eye, and 

 we must absolutely confine our observations to the vultures. Mere 

 theorizing would never open up the conception of sailing fiight; more 

 over, we may consider it a dead letter when human life is to be risked 

 in experiment. The moral result of observation is inliiutelv more con- 



