398 



NA TURE 



[August 21, 1890 



a new circle begins identical with the first one, if the 

 absolute velocity in/is the same as that in a, which docs 

 not imply any impossibility, even including the resistance 

 of the air to the advancing. It is, however, important 

 that the increment of velocity during the course a-b-c, 

 is equal to its diminishing during the course c-e-f. 

 Certainly the resistance of the air caused by the wind 

 is greater during the latter part of the course than during 

 the former, but the way is shorter in which this greater 

 resistance is working. 



In which plane or in which planes the different parts of 

 the course will pass depends upon the initial velocity and 

 upon the changes of the relative velocity of the bird ; 

 naturally also upon the invariable quantities — the weight 

 of the bird, the size and form of the wing plane, so far 

 as the latter has influence upon the resistance of the air 

 to the advancing. Now in a and/the relative velocity is 

 the same as the absolute or minimal velocity. In c the 

 relative velocity is also the same as the absolute velocity, 

 but in c they are both greater than in a andy^ as we have 

 shown here above. Thus the relative velocity has in- 

 creased during the course n-b-c. During the courses to b 

 no increment has occurred, on the contrary ; so much the 

 faster has it increased during the course b to c. During the 

 course ^: to ^ the relative velocity increases continually, 

 and obtains near e its maximum ; whereas it gradually 

 diminishes during the course ^ to /, so as to equal the 

 initial velocity. Suppose then that the relative velocity 

 diminishes somewhat during the course a to d. This 

 diminution, however, will be over-compensated during the 

 course b to c, the relative velocity in c being greater than 

 that in a. During the whole course c-e-f, the relative 

 velocity is greater than in a and/ Surely the supporting 

 power of the current of air on the wings depends upon 

 the relative velocity. It increases with the relative 

 velocity, if we suppose everything else to be unchanged, 

 particuhrly the angle of inclination of the wing-plane. 

 If, therefore, the initial velocity in a by a certain pointing 

 of the wing-plane is only just sufficient to maintain the 

 bird at an unchanged level, the bird must, when describing 

 the course a to (5, gradually drop down. Even on the other 

 side of b the sinking is continued until the relative 

 velocity has increased so as to regain the same value as 

 in a. From this point the course begins to rise and will 

 continue rising until / for to this point the relative 

 velocity is greater than in a. Under such circumstances 

 we cannot be astonished if the part / of the course will 

 be in a higher plane than the part a, even if the resistance 

 of the air to the advancing is infinitesimal. 



Should the initial velocity in a be greater than what is 

 required to maintain the bird on the same level, the bird 

 would already there have a rising course, and it might 

 easily happen that no part of the course would be de- 

 scending. However, the resistance of the air increases 

 much faster than the relative velocity, and therefore the 

 most available initial velocity will be different for different 

 birds and for different force of the wind. It is not as yet 

 an easy matter to calculate the most favourable initial 

 velocity to certain birds and to certain winds. But the 

 discrepancies in the descriptions of the forms of the 

 circles find, as may easily be seen, their explanation in 

 supposing a different initial velocity. This is likely to be 

 chosen differently by different birds, and may be different 

 for the same bird according to different force of wind. 



I am convinced that the bird always, even when 

 soaring with the wind, has a greater velocity than the 

 wind, and that thus during this part of the circle his 

 speed is not hastened by the wind, but on the contrary he 

 is here delayed, maybe less than in the other parts of the 

 course. On the other hand, the velocity of the bird is 

 augmented by the wind, as soon as the wind catches the 

 bird from the side or obliquely from behind. This gain 

 of velocity covers the loss caused by the resistance of the 

 air to the advancing, and consequently allows the bird to 



NO. 1086, VOL. 42] 



maintain the necessary average velocity. It is less ob- 

 vious, but nevertheless very likely, that the soaring bird^ 

 having gained the necessary velocity and having pointed 

 his wings suitably, can, without changing the form of his 

 wings, incessantly continue the soaring, as long as the 

 force of the wind is unchanged. 



Mr. Peal's 1 explanation no doubt comes nearest the 

 truth, when he compares the soaring bird to a kite. We 

 may consider the bird a kite, but the string which 

 connects him with the earth is not fixed at a point of the 

 surface of the earth, but the point of fastening moves 

 with the wind, though it may be slower than the wind. 

 It is the difference of velocity between the motion of the 

 fastening-point and that of the air which affords the 

 necessary power for the support and the rising of the 

 t>'rd. Magnus Blix. 



Lund, Sweden. 



ELECTROLYSIS OF ANIMAL TISSUES. 

 A PRELIMINARY account of part of the work was 

 ■^^^ given in the Proc. Roy. Soc. Edin., 1888, and a 

 short description of later results at a meeting of the 

 Physiological Society at Cambridge in March last. The 

 full paper is being published in a volume of memoirs 

 from the physiological laboratory of the Owens College, 

 Manchester. The chief results are here summarized. 



(i) The first part of the research was directed to 

 answering two questions : {a) Is the cotiductlon in animal 

 tissues entirely or chiefly electrolytic ? {b) What are the 

 electrolytes ? It is shown that by far the greatest part of 

 the conduction at any rate is electrolytic, and that the 

 best conductors by far are the inorganic constituents of 

 the tissues. Next to these, but at a great distance, come 

 some of the nitrogenous metabolites. The proteids are 

 exceedingly bad conductors. 



(2) The changes p7 educed in simple proteid solutio7is 

 were next investigated. It is shown that the proteids are 

 affected not by primary electrolysis, but by the products 

 of electrolysis of the salts. 



The effects vary to some extent with the current 

 density. In solutions of coagulable proteids alkali- 

 albumin is formed at the cathode, and acid-albumin 

 at the anode, some of the proteid being coagulated at 

 the latter. 



(3) The eflects of electrolysis on isolated tissues and on 

 some of the liquids of the animal body. 



Striped Muscle. — Great changes were found in the 

 microscopic appearance of the fibres. The nuclei be- 

 came very prominent in those near the anode, with 

 apparent coagulation of the sarcous substance, suggesting 

 the action of a dilute acid. At the cathode the fibres 

 were more homogeneous than before. The striation was 

 impaired. Chemically, the same changes in the proteids 

 were found as in simple proteid solutions, and a distinct 

 effect on the distribution of the salts was made out, by 

 estimating the ash in different parts of the muscle. 



Blood. — Entire defibrinated blood, blood serum, and 

 pure haemoglobin solutions were used. There was no- 

 indication that haemoglobin, or any derivative of it, acts 

 the part of an ion. At the anode the reaction becomes 

 acid, and acid-hsematin is formed, which remains partly 

 in solution and is partly thrown down, the solution 

 becoming less deeply coloured. When the current is 

 strong or long continued the haematin suffers further 

 change and is decolorized, apparently by the oxygen 

 or chlorine set free. If a reducing agent is present at 

 the anode, the haemoglobin there is not affected by the 

 electrolysis. At the cathode alkali-haematin is ulti- 

 mately formed, although its less definite spectrum does 

 not show itself so soon as that of acid-haematin at the 

 anode. . The proteids of the serum and corpuscles are 



' Nature:, vol. xx'ii. p. lo. 



