December 14, 191 1] 



NATURE 



217 



ft 



Theorems on stresses in envelopes by Mr. Booth. 



Forces and couples on a model dirigible placed 

 obliquely to the current by Mr. Bairstow. 



Air resistances of wires and ropes, both stationary 

 and vibrating, by Mr. Melvill Jones and Dr. Stanton. 



Air pressures on the honeycombed radiator and 

 Paulhan girder. 



Methods of observing flow of water past an obstacle 

 by Mr. Eden. 



Propeller experiments by Mr. Bairstow. 



Tests of balloon fabrics. 



Meteorological apparatus by Mr. J. S. Dines. 



The present report is characterised by greater de- 

 finiteness of purpose than was noticeable in its pre- 

 decessor for 1909-10. Many of the papers have a 

 direct bearing on aerial navigation, and we do not 

 exclude Mr. Bairstow 's experiments on square plates 

 altogether from this category, since if it is required 

 to test the deviations from the law of proportion of 

 pressure to square of velocity, the first tests may as 

 well be made on square plates as on any other kind 

 of surface. The experiments on obliquely placed 

 model dirigibles also have an important bearing on 

 the problems of stability and steering as applied to 

 airships, and the necessity for such investigations is 

 fairly evident. At the same time, the superfluity of 

 diagrammatic details which was referred to in the 

 review of the preceding year's report is also to some 

 extent a conspicuous feature of the present volume, 

 and it again appears desirable to direct attention to 

 the fact that some of these are wholly unnecessary 

 and only occupy space that could be with greater 

 advantage devoted to broad and general discussions 

 by the members of the committee on the principles of 

 mechanical flight, considered in relation to the experi- 

 ments here described. The three and one-third pages 

 of description of Mr. Dines's theodolite would prob- 

 ably be just as useful without the three folded 

 diagrams, one taken at Pyrton Hill in a clear sky, 

 and one showing the observations by Cary at station 

 A, and Bosch at station B, up to the point where a 

 certain pilot balloon was lost sight of. 



The article on propellers, while accompanied by 

 six bulky folding plates, only occupies four pages of 

 letterpress. One of these is devoted to " improvements 

 in .'i]:)paratus " — not improvements in propellers, but 

 in the dynamometers and other instruments for testing 

 them, while the remainder are principally devoted to 

 determining the constants and coefficients of a Vickers 

 and Maxim, and three Ratmanoff propellers. Certain 

 conclusions are stated, referring in particular to the 

 effects of cutting down the blade area, and the extent 

 to which the principle of similarity can be applied to 

 models. But surely there is a great deal more to be 

 said about the general problem of propeller action, 

 even in connection with the interpretation of the 

 results of these experiments, and it is desirable that 

 <iir> investigation should be extended to other types 



propeller than the two here discussed. Perhaps 



- will be done another 3'ear. 



In making these criticisms it is necessary to guard 

 i^^ainst one serious mistake which is commonly made, 

 and does much to retard scientific progress and 

 d'velopment. Tt. is frequently said of certain phvsical 

 investigations that they are of no use because they 

 do not take into account all the disturbing factors 

 which exist in nature. As applied to aviation, we 

 are told by some people that it is no use to investigate 

 the efTiciency of planes and propellers by laborator\' 

 experiments, as the investigations fail to take account 

 "^ the atmospheric disturbances which affect the 



ition of an actual aeroplane. This, however, is 

 ■ univalent to saying that we require to know less 

 'bout the efficiency of our apparatus under the com- 



NO. 2198, VOL. 88] 



plex conditions prevailing in nature than we should 

 if the conditions were simpler. In reality we ought 

 to know- more, and experiments made under ideal con- 

 ditions instead of being condemned as "unnecessary," 

 should be described as '" insuflicient," and should there- 

 fore be pushed on with all possible haste as a pre- 

 liminary step to investigations of a more general 

 character. 



In view of the desirability of using experiments 

 with models for all they are worth, and the success 

 which has attended such experiments in naval archi- 

 tecture, it is satisfactory to find that the principle of 

 dynamical similarity is receiving considerable atten- 

 tion. At the same time, one has rather an idea that 

 the atmospheric conditions under which aeroplanes 

 and dirigibles are navigated are rather different from 

 those existing in the National Physical Laboratory, 

 and the idea suggests itself that, instead of trying to 

 produce a current of air that shall be as nearly 

 uniform as possible, results equally interesting would 

 be obtained if it were attempted to do the very oppo- 

 site thing, \yhen so many physical data are unknown 

 even to within 100 per cent., it surely is rather un- 

 necessary to trouble about whether a velocity of i"6 

 or 2' I miles an hour is set up in the air when a rotat- 

 ing arm is travelling through it at thirty-five miles an 

 hour. A study of the "wash" or interference effects 

 caused by planes or propellers on other planes or pro- 

 pellers following in their wake would be more useful. 

 For example, the lift and drift of the isolated Paulhan 

 girder determined on p. 36 may for this reason be 

 different from the values which. they would have when 

 the girder occupied its proper place in an actual 

 flying-machine. 



There are two possible alternatives. One is (follow- 

 ing the usual custom) to disparage such researches as 

 tliose last-named; the other is to ask for something 

 more. The latter alternative certainly appears from 

 every point of view to be the better. 



The collection of abstracts of papers on aeronautics, 

 compiled from various English and foreign journals, 

 extends from p. 92 to p. 124, and is an exceedingly 

 valuable feature of this, as it was of last year's report. 

 The preparation of such abstracts involves an expen- 

 diture of time and thought, on the part of the 

 abstractors, which, as a rule, receives but scanty 

 recognition. The idea suggests itself whether some 

 working arrangement could be arrived at between the 

 Government Committee and the Aeronautical Society 

 to enable the abstracts to be reprinted in the Journal 

 of the latter, and thus circulated among its members 

 at regular intervals. Perhaps this question may be 

 deferred until the Aeronautical Society has had time 

 to settle down after the arduous work of reorganisa- 

 tion on which its council has recently been engaged. 



SIGHT TESTS IN THE MERCANTILE MARINE. 



THE Board of Trade has published the annual 

 return of the sight tests used in the mercantile 

 marine for the year ending December 31, 19 10 (Par- 

 liamentary Paper, Cd. 5876), a return which includes 

 the examinations in both form and colour vision. In 

 the course of the year 7502 candidates were examined, 

 including fishermen who sought to obtain cer- 

 tificates as skipper or second hand of fishing boats, 

 and of this total 109 (i'46 per cent.) failed in form 

 vision, and one of them, who was re-examined, failed 

 again. One hundred and forty-one failed in colour 

 vision, but of these 69 were re-examined on appeal, 

 and 29 of them passed, lonving T12 (i'56 per cent.) as 

 ultimate failures. 



The colour examination, ^ince November, 1909, has 

 been conducted with five skeins of wool, a purple and 



