S. P. Lanyley — Internal Work of the Wind. 61 



wiDd of considerably differing velocity (such as the anemome- 

 ter observations show, are realized in nature), that the same 

 general effect will obtain,* though we are not entitled to 

 assume from any demonstration thus far given that the total 

 advance will be necessarily greater than that of the whole dis- 

 tance the mean wind has traveled. It may also be observed 

 that the actual actions of the soaring bird may be and doubt- 

 less are, more complex in detail than those of this diagram, 

 while yet in their entirety depending on the principles it sets 

 forth. 



The theoretical possibility at least will now it is hoped, be 

 granted, not only of the body's rising indefinitely, or of its 

 descending in the interval of calm to a higher level C, than it 

 rose from at A, but of its advancing against the calm or light 

 wind through a distance BC, greater than that of A B, and so 

 on. The writer however repeats that he has reason to suppose 

 from the data obtained by him, that this is not only a theoret- 

 ical possibility, but a mechanical probability under the condi- 

 tions stated, although he does not here offer a quantitative 

 demonstration of the fact, other than by pointing to the move- 

 ments of the soaring-bird and inviting their reconsideration in 

 the light of the preceding statements. 



The bird, by some tactile sensibility to the pressure and 

 direction of the air, is able, in nautical phrase, to u see the 

 wind "f and to time its movements, so that without any refer- 

 ence to its height from the ground, it reaches the lowest por- 

 tion of its descent near the end of the more rapid wind pulsa- 

 tion ; but the writer believes that to cause these adaptive 

 changes in an otherwise inert body, with .what might almost 

 be called instinctive readiness and rapidity, does not really 

 demand intelligence or even instinct, but that the future pro- 

 drome may be furnished with a substitute for instinct, in what 

 may perhaps allowably be called, a mechanical brain, which 

 yet need not, in his opinion, be intricate in its character. His 

 reasons for this statement, which is not made lightly, must 

 however be reserved for another time. 



It is hardly necessary to point out that the nearly inert body 

 in question may also be a human body, guided both by instinct 



* The rotation of the body about a vertical axis so as to change the aspect of 

 the inclination as in the first figure, may be illustrated by the well-known habit 

 of many soaring-birds, of moving in small closed curves or spirals, but it may 

 also be observed, in view of the fact that even in intervals of relative calm during 

 which the body descends, there is always some wind, — that in making the descents, 

 if the body, animate or inanimate, maintain its direct advance, this wind tends to 

 strike on the upper side of the plane or pinion. Mr. G. B. Curtis offers the sug- 

 gestion that the soaring-bird avoids such a position when possible, and therefore 

 turns at right angles to or with the wind, and that this may be an additional 

 reason for his well known habit of moving in spirals. 



f Mouillard. 



