August io, 191 i] 



NATURE 



181 



London we have reared very considerable numbers of 

 E. miliaris from the egg through the metamorphosis. The 

 eggs were fertilised in the beginning of April, and when I 

 left London in the middle of June there were many young 

 Echini creeping about. The details of the methods adopted 

 will be described in a paper shortly to appear in The 

 Quarterly Journal of Microscopical Science. Last year we 

 reared the eggs of the Serpulid Pomatoceros until the larva; 

 had attained the adult condition and had formed tubes, 

 which were attached to the sides of the vessel in which 

 they were. E. W. MacBride. 



Marine Biological Association of the West of 

 Scotland, July 28. 



FLIGHT, NATURAL AND ARTIFICIAL.' 

 TN the words of the introduction, "The object of 

 -*■ this report is to place at the disposal of the 

 members of the society some of the information now 

 available regarding the physical characteristics, powers 

 of flight, &c, of birds. It must be clearly understood 

 that, owing to the great difficulty experienced in col- 

 lecting the details of weights, wing area, &c, the 

 report is of a temporary nature only, and does not 

 profess to give the fullest possible information regard- 

 ing the subject dealt with. The details given, how- 

 ever, have been taken from the best available sources, 

 and it is hoped that the report as a whole will be 

 found a useful introduction to the study of bird flight." 

 It will be seen that original observation and experi- 

 ment did not fall within the scope of the committee, 

 but, subject to this and the other limitations men- 

 tioned above, the results of their labours cannot fail 

 to be of value. 



The first section deals with the classification of 

 birds from (a) the ornithological and (b) the aero- 

 nautical point of view. Under (a) table i. gives a 

 classification after Finn into twelve main groups, 

 further subdivided into families. The aeronautical 

 classification presents difficulties. In table iii., 

 column 17, are given the values of S=/W 4 , S being 

 the surface and W the weight, together with other 

 particulars for a large number of birds. 



Section ii. is devoted to a description of the prin- 

 cipal sorts of flight and of various manoeuvres, such 

 as turning in the air. Under the first head are men- 

 tioned gliding flight, flapping flight, and soaring 

 flight, of which, however, the first does not differ 

 essentially from the third. Instructive photographs 

 after Marey and Milla are reproduced. Soaring has 

 been the subject of much discussion at various times, 

 no small part of it being hopelessly confused by mis- 

 understanding of mechanical principles. Even in the 

 present section paragraph 12 is not above reproach. 

 The comparison of soaring with the normal perform- 

 ance of a sailing ship is certainly misleading. 



When a bird maintains or increases his elevation 

 without working his wings, the explanation is to be 

 sought in a special movement of the air. It cannot 

 be too much emphasised that for this purpose a 

 uniform horizontal wind is of no avail. The larger 

 soaring birds, such as condors and pelicans, probably 

 find their support on ascending currents. Such cur- 

 rents must exist, though we on the ground perceive 

 little of them. Even though the wind be strictly hori- 

 zontal in the space where the bird is flying, advantage 

 may be taken of variation with height or with time. 

 As a matter of fact, the wind, near the ground at 

 any rate, is always more or less gusty. 



Travellers at sea have frequent opportunity of 

 making interesting observations. In these latitudes 

 one may see gulls following the ship and taking ad- 

 vantage of upward currents deflected from the sails 

 or hull. From other parts of the world the albatross 



1 Aeronautical Society of Great Britain. F.rst Report of the Bird Con- 

 struction Committee. Compiled by Col. J. D. Fullerton. Pp. 61. (London : 

 Aeronautical Society of Great Britain, torr.) Price 10s. 6d. net. 



NO. 2l8o, VOL. 87] 



is often reported to follow the ship, maintaining his 

 position for minutes or hours together without flap- 

 ping of wings. Since in this case the distance from 

 the ship may be considerable, one must appeal to 

 upward currents deflected from the waves or to the 

 other specialities of wind already mentioned. But is 

 it certain that a flapping of the wings could not 

 escape attentive observation? One would have sup- 

 posed so; but the evidence is not free from ambiguity. 

 Following upon a lecture upon the mechanical prin- 

 ciples of flight, given in 1900, 1 a correspondent sent 

 me an instantaneous photograph of an albatross flying 

 "very near indeed" to the ship. In the picture the 

 wings appear elevated as if near the top of a stroke, 

 but to the observers at the time "the wings were fully 

 extended in a line with the body." In answer to 

 further inquiries my correspondent wrote: "■Without 

 question none of the many passengers who were 

 watching the albatross (which was exceptionally near 

 the side of the ship) saw the slightest movement of 

 the wings when I took my snap-shot. To all appear- 

 ance they were fully extended and immovable — cer- 

 tainly 10 to 12 feet from tip to tip." Here, indeed, 

 is a question worthy of further attention from travellers 

 in the southern seas. 



Section iii. of the present report deals with weight, 

 wing area, &c. The heaviest bird in the table is the 

 Californian vulture, weighing 136 kilog. (30 lb.). 

 The bird carrying the greatest weight per sq. m. 

 is the whooper swan (2i'3 kilog. per sq. m.). In 

 section iv. we find observations and calculations 

 regarding the velocity of birds, the power expended, 

 &c. It appears that the maximum speed in ordinary 

 flight does not much exceed 50 miles per hour, and 

 that no bird moving near the earth's surface attains 

 the enormous speed with which flying creatures are 

 sometimes credited. These speeds are, of course, 

 relative to the air. At considerable heights migrating 

 birds may easily experience winds of like amount, so 

 that 100 miles per hour, or more, relative to the 

 ground may well be admissible. 



The opinion is expressed that the power required 

 for flapping flight has been much exaggerated. This 

 may be true as regards regular horizontal flight, but 

 it remains a fact that the power exerted by some 

 birds, e.g. pigeons, in rising nearly vertically is very 

 great. The question was discussed by Penaud in 

 1876. " In the ascent the total work developed by the 

 bird is divided into two parts, the one fixed, that is, 

 the work of elevation ; the other variable and increas- 

 ing with the time, that is, the work dispensed in 

 finding a support in the air." 



" It is thus to the interest of the bird to rise as 

 quickly as possible, which it generally does, even 

 when under no sense of fear. Their velocity of direct 

 ascent is always several yards per second." And, 

 further : " Thus, and apart from all theory, it is 

 certain that birds are capable of developing momen- 

 tarily a force corresponding at least : for the peacock, 

 to 1 horse-power for every 66 lb., and for the pigeon 

 and ring-dove. 57 lb." ; and, as before mentioned, the 

 work of elevation is not the whole. 



In these days there is a natural tendency to over- 

 look the work of the early pioneers. In principle 

 not much has been added to the conclusions of Wen- 

 ham and Penaud, and the latter constructed actual 

 flvinq--machines. What was wanted to make flight 

 practical was the advent of the light motor, as de- 

 veloped for the motor-car. When this became avail- 

 able, the skill and courage of such men as the brothers 

 Wright soon led to successful human flight. Further 

 progress is assured, but how far it will go would 

 require a bold man to prophesy. Rayleigh. 



Manchester Memoirs, yli v ., p. 1 ; Scientific Papers, iv., p. 46? 



