248 



NA TURE 



[August 26, 1909 



Model Screws," R. E. Froude, F.R.S., Proc. Naval 

 Architects, iqoS). 



Among birds, those which fly continuously seldom 

 have the" ratio of weight to wing area more than i lb. 

 per square foot, and in many cases, such as hawks 

 and swallows, the ratio is something like \ lb. per 

 square foot; but whatever the ratio mav be, so 

 long as the animal can only give out a limitea amount 

 of power proportional to its weight, a definite limit 

 can be assigned to the size and weight of the body 

 which can sustain itself in flight by muscular action. 



If the weight of the wing increased directly as its 

 area such a limit would not exist. The weight of a 

 flock of birds, for example, is limited simply by the 

 numbers in the flock, and we only have to suppose the 

 individuals to be connected by a light framework to 

 convert the flock into a flying machine the wing 

 weight of which is proportional to the wing area. To 

 a certain extent, the biplane flying machine carries 

 out the same idea, but in most of the existing types 

 the weight of the connecting framework must to a 

 great extent neutralise the reduction of weight which 

 should accompany the reduced linear dimensions. 



From what has been said it will be seen that so 

 long as no engine was available which, with all 

 adjuncts, such as fuel supply, framing, and wings, 

 could raise the total weight much faster than could 

 an animal of the weight of the engine only, there 

 was no chance for the addition of flight to human 

 accomplishments, and it is due to the advent of the 

 internal-combustion engine that it is now possible to 

 carry air-borne loads of more than looo lb. To carry 

 heavy loads with a moderate wing area requires large 

 horizontal velocities, and in such machines as have 

 succeeded the load per square foot generally exceeds 



2 lb. 



The high velocity requisite is advantageous when 

 the machine is launched and is pursuing a straight 

 course, but it adds to the difficulties of starting and 

 stopping, and is a restriction on manoeuvring power : 

 that is, it increases the radius of the circle in which 

 the machine can turn. When a flying machine of 

 weight w travels in a circle of radius r with velocity 

 V the centrifugal force, F, is wv'/rg, and if the plane 

 of the circle is horizontal the upward component of the 

 normal force on the wings is w, and hence the normal 

 force is (ui'-l-F")» (nearly), and the inclination (j8) of 

 the wings to the horizontal in the direction of r is 

 F/w. 



The normal force on a straight course differs little 

 from w. In flying in a horizontal curve, therefore, 

 the normal force must be increased in the ratio 

 {iu- + F-)i/iv if the velocity is to remain constant. To 

 effect this the engine revolutions must be quickened 

 and the fore and aft trim of the wings altered. In 

 other words, it requires more power to fly in a curve 

 than in a straight course at the same speed, although 

 the increase is not important so long as FJiv is small. 



For example, if v = ^o f.s. and r = 2oo feet, 

 F/iy = o'256, the increase of power required is about 



3 per cent., and 5 = 14°. For the same radius if 

 ^=100 f.s., F!w=i'-,6. The power required is i'S6 

 times that for the straight course, and /3 = 56° about. 



I am not aware that any exact experiments have 

 yet been made on the manoeuvring capacity of flying 

 machines, but the subject will have to be carefully 

 investigated. 



The three most important lines along which the 

 development of flying machines should be pursued are 

 those relating to intrinsic stability, ease of starting 

 and stopping, and manoeuvring capacity. It is im- 

 probable that any form is intrinsically stable at all 

 speeds, but automatic devices may be introduced (as 

 mentioned in my letters to Nature of January 30 and 



NO. 2078, VOL. 81] 



December 24 1908) which will relieve the aeronaut 

 of responsibility in this respect. Ease in starting and 

 stopping implies the power of flying (at any rate, for 

 a short time) at low velocities; while manoeuvring; 

 capacity demands ready control of the angles at which 

 the various supporting surfaces are presented to the 

 air. A. Mallock. 



THE BRITISH ASSOCIATION AT WINNIPEG. 



AS we go to press the seventy-ninth annual meeting, 

 of the British Association is being opened at 

 Winnipeg, under the presidency of Sir J. J. Thomson, 

 F.R.S., whose inaugural address is reprinted below. 

 Following our usual custom, the addresses of presi- 

 dents of most of the sections will be published in 

 future issues of Nature, and also accounts of the 

 scientific proceedings of the sections. 



This is the fourth time the association has met out- 

 side the British Isles, the previous occasions being 

 Montreal (1884), Toronto (18,97), and South Africa 

 (1905). The last meeting of the association in Canada 

 was very successful, the number of members and asso- 

 ciates present being 1362. During the twelve years 

 that have since elapsed, great progress has been made' 

 in all branches of science, and, though the people of 

 Western Canada do not expect to contribute a very- 

 large part to the scientific proceedings of the sections, 

 they anticipate interest in many of the subjects to be 

 dealt with or discussed. Much interest in the meet- 

 ing has been manifested in Canada and the United 

 States, as well as on this side of the Atlantic. It is. 

 estimated that between 400 and 500 members have 

 gone to Winnipeg from Europe, and it is hoped that 

 the total number of members and associates attending 

 the meeting will be at least 1500. 



Generous financial support towards the expenses of 

 the meeting has been given by the Dominion Govern- 

 ment, the Government of Manitoba, and the city of 

 Winnipeg, while the western provinces and cities have 

 agreed to defrav the e.xpenses of an excursion to the 

 Pacific Coast of a party of about two hundred office- 

 bearers and distinguished guests of the association. 



Excursions have been arranged for Saturday, 

 August 28, to points of interest in the vicinity cf 

 Winnipeg, including Stony Mountain and the muni- 

 cipal stone quarries; Lake W'innipeg, St. Andrew's 

 Rapids, and Selkirk ; the wheat fields of Manitoba ; 

 the hydro-electric plant on the Winnipeg River. 

 Members have also the opportunity of visiting various 

 industrial works in the city of Winnipeg. 



Evening receptions will be held by the Lieutenant- 

 Governor at Government House, and by the loca': 

 executive committee. Garden-parties have been 

 arranged for several afternoons during the meeting 

 including those to be given at the historic Lower Fort 

 Garry by the Commissioner of the Hudson's Bay 

 Company, at the Provincial Agricultural College, and 

 by the Hon. Chief Justice Howell. 



Inaugural Address by Prof. Sir J. J. Thomson, M.A., 

 LL.D., D.Sc, F.R.S., President of the Association. 

 Twenty-five years ago a great change was made in the 

 practice of the British Association. From the foundation 

 of our Society until 1884 its meetings had always been 

 held in the British Isles ; in that year, however, the 

 Association met in Montreal, and a step was taken which 

 changed us from an Insular into an Imperial Association. 

 For this change, which now I think meets with nothing 

 but approval, Canada is mainly responsible. Men of 

 science welcome it for the increased opportunities it gives 

 them of studying under the most pleasant and favourable 

 conditions different parts of our Empire, of making new 

 friends ; such meetings as these not only promote the 



