﻿HuTTON. —On the Flight of the Alhatros. 349 



Page 235, line 21, et seq. — " Captain Hi;tton goes on to say * the total 

 amount tlie bird will rise will be LE + HA feet.' Introducing tbe corrections 

 just made, tliis amounts to saying that the upward pressure on the whole area 

 of the bird = HE (sin AEH + sin CEH). This is a grave error." 



No doxibt it is, with Mr, Webb's additions and corrections, a very grave 

 error indeed, but it is not of my making. The same confusion that has 

 already been pointed out is again here very apparent. " The total amount 

 the bird will rise," is not by any means the same thing as " the upward 

 pressure on the whole area of the bird," although Mr. Webb has substituted 

 one for the other. HE, HA, and LE, do not represent pressures, but spaces 

 traversed in a certain time, or, in other words, velocities. As HE was origi- 

 nally taken to represent the velocity of the bird, or air (which must be the 

 same thing), it could not possibly also represent the force or 'pressure of the air, 

 which is a very different thing, although Mr. Webb has taken it to represent 

 hoth. At the outset of my calculations I changed the pressure necessary to sup- 

 port the bird into an upward current of air moving with a velocity of 30 feet per 

 second, and the problem then was to find what would be the horizontal velocity 

 (HE) of the air which would give, when acted upon by the wings of the bird, a 

 vertical comjDonent equal to 30. I then showed that when the bird was flying at 

 an angle (AEH) with the horizon, the distance it would rise in a second (HE tan 

 AEH) would have to be deducted from the 30. I next showed that when the 

 velocity of the wind was HE, its vertical component, when acted on by the 

 wings of the bird inclined at an angle CEH to the horizon, would be HE sin 

 CEH cos CEH, and that, therefore, the two must together be made equal to 

 30 to enable us to find what the horizontal velocity of the wind (HE) 

 should be, in order that it might just counteract the force of gravity. I must, 

 however, here confess that, owing to a lapsus calami, I have, imfortunately, 

 written in my paper " the force of the wind HE," instead of " the velocity of 

 the wind HE," and twice afterwards, where the word "force" has been 

 employed, it would jDerhaps have been better to have used the word " direction," 

 and although this slip has in no way affected my subsequent reasoning, it may 

 have confused Mr. Webb and led to his mistakes. So far, therefore, I must 

 plead guilty, but I cannot allow that he has uj:)set any conclusion that I have 

 drawn ; on the contrary, he has supplied me with a formula, which, as I shall 

 presently show, completely gets over the only difficulty in the way of my 

 theory. 



Mr. Webb's equation (1) is not correct, for, as I have shown, HE sin AEH 

 and HE sin CEH are not the vertical components of the resistance of the air, 

 and equation (2) is not a legitimate deduction from (1), as in it force and 

 velocity are confused together, consequently (3j and (4) are incorrect also. 



T agree with Mr. Webb that it is hardly fair to couiparc an Albatros with 



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