5IO 



NATURE 



[January 6, 191 6 



In addition to the constant torque of the propeller, 

 and the gyrostattc effects due to its rotatory inertia, the 

 propeller introduces a number of additional terms into 

 the resistance derivatives, thus mixing up the longi- 

 tudinal and lateral oscillations. I propose that a theo- 

 retical basis of comparison should be worked out for 

 these coefficients by treating the propeller blades as 

 " narrow planes gliding at small angles " in a medium 

 the resistance of which follows the sine law. What- 

 ever objections may be raised to this assumption, it 

 will at any rate lead to some definite conclusions with 

 which results of experiment can be compared. 



I have for a long time past expressed the hope that 

 it may be found possible to develop the tandem pro- 

 peller with blades rotating in opposite directions, the 

 rear propeller having the higher pitch. 



Practical experts state that the system has proved 

 a failure. It would be interesting, however, to learn 

 whether this is because there is no perceptible gain of 

 efficiency, or whether there is really a serious loss of 

 efficiency. To get rid of the unsymmetrical action of 

 the propeller would be worth some sacrifice of 

 efficiency. 



Mr. R. Jones, late of this college, who is now 

 working with Mr. Bairstow in the National Physical 

 Laboratory, has just contributed a paper to the Royal 

 Society on motion of a stream of finite breadth past a 

 body (see Nature for November ii, p. 304). 



It will thus be seen that while we are making a 

 fresh start in the study of the rigid dynamics of aero- 

 plane motions, more recruits are needed if we are to 

 arrive at anything approaching a clear understanding 

 of the subject before the end of the war. In the mean- 

 time every aeroplane is to be regarded as a collection 

 of unsolved mathematical problems ; and it would have 

 been quite easy for these problems to be solved years 

 ago, before the first aeroplane flew. I have seen no 

 reference to aeroplanes in connection with Section A 

 of the British Association ; and this in war-time ! It 

 would be quite impossible for me in the circumstances 

 to divert my attention to the practical aspects of 

 aviation, for to do so would only add to the collection 

 of unsolved problems. It therefore became necessary 

 for me to resign from the committee of the association 

 Mr. Blin Desbleds is endeavouring to form, and it is 

 further necessary for me to disclaim any connection 

 with a Government committee such as has been re- 

 cently announced in certain sections of the Press. 



G. H. Bryan. 

 University College of North Wales, Bangor. 



Belated Migrants. 



It may be of interest to the ornithological readers 

 of Nature if I place on record that on the morning of 

 December 27, just as the gale of the previous night 

 was abating, and in a gleam of sunshine that broke 

 through for nearly half an hour about 10.30, I observed 

 against the blue sky a flock of birds flying over Wilton 

 Park (on which my house gives) with a very herundine 

 flight. They were excitedly disporting in the wind, 

 wheeling and gyrating, just as they do so often prior to 

 their autumn migration. At first I thought they must 

 be starlings ; but on their coming close overhead the 

 white in their plumage showed them to be martins. 

 There were from a dozen to a score of them, and they 

 were moving in a northerly direction ; but as I was 

 starting to catch a train, I could not, to my regret, 

 watch them longer, and that bearing may not be the 

 course they afterwards pursued. Whence had they 

 come, and whither were thev bound? 



It may be perhaps also worth mentioning that for 

 the past fortnight our hedgerows here and the Wilton 

 and Burnham woods have been quite resonant with the 

 NO. 2410, VOL. 96] 



spring songs of many species of birds. The thrush 

 and the blackbird have been especially vociferous for 

 more than a week, each day adding to the melodious- 

 ness of their song. The latter have been engaged, 

 often half a dozen at a time, in quite spectacular love- 

 tournaments in my garden — where the snowdrops are 

 already some time in flower — for nearly three weeks 

 past. Now and again a soaring lark also fills the air 

 with his melody. May such early harbingers of spring 

 presage a new year "happy and victorious"! 



Henry O. Forbes. 

 Redcliffe, Beaconsfield, Bucks, January i. 



The Popularisation of Science. 



I HAVE read with interest the several articles you 

 have recently published on the position of science in 

 England, and would like to be allowed to make a 

 few remarks on the subject. 



It is scarcely surprising that scientific knowledge 

 is so little disseminated in this country considering 

 the difficulties which hinder its acquisition. If science 

 is to become widespread, it seems to me essential 

 that it should be democratic both in its higher and its 

 lower branches. In England, however, science may 

 be said to be aristocratic. Scientific societies de- 

 mand more or less high subscriptions. Public lec- 

 tures on science are rarely free. In London an insti- 

 tution exists where advanced lectures are given, but 

 the subscription to which is considerable, and to be- 

 come members of which people have actually to be 

 recommended — recommended to be allowed to learn ! 



\x\ France matters are different. The membership of 

 scientific societies is moderate, and higher scientific 

 education is provided gratuitously by the State at the 

 College de France, the Sorbonne, and elsewhere. 

 There are many instances in France of men devoting 

 themselves to research from purely intellectual motives, 

 and in most classes in that country the scientific spirit 

 is displayed. F. Carrel. 



Bath, December 16. 



THE EXPORT OF FEEDING STUFFS AND 

 FERTILISERS. 



r3 ECENT correspondence in the Times has re- 

 -'-^ vealed a certain amount of uneasiness at the 

 export from this country of fertilisers, linseed cake 

 and other feeding- stuffs, which go to neutral 

 countries, but, it is sug-g-ested, do not stop there, 

 as the quantities are in excess of normal con- 

 sumption. It is urg^ed on one hand that the 

 proper maintenance of the balance of trade re- 

 quires the export of as many commodities as 

 possible, and, on the other, that any fertilisers and 

 feeding stuffs which found their way to enemy 

 countries would obviously prove extremely 

 valuable to them. 



The fertiliser mainly concerned is sulphate of 

 ammonia. About 400,000 tons of this are normally 

 produced here each year, of which 300,000 are 

 exported, Japan taking- about 100,000 tons, Spain 

 60,000, the Dutch East Indies and the United 

 States each about 40,000 tons, and so on. Hol- 

 land only takes a little : no more than 3000 to 

 3500 tons per annum. At the present time forei.<?n 

 shipments are of course only allowed under licence, 

 but it is stated on the authority of a trade publi- 



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