July 13, 191 1] 



NATURE 



63 



by a graduated series of tests on a number of bags of a 

 specially selected fabric. 



In the above tests it was found that bags of parallel 

 doubled material and of the same material diagonally 

 doubled appear to be of nearly the same strength for a 

 1 : 1 ratio of stresses, while the tensile strength of the 

 fitter determined in the usual way is only half that of the 

 former. 



An account is also given by Mr. O'Gorman in the tech- 

 nical report of a large number of bursting tests carried out 

 at the Army Aircraft Factory on a variety of fabrics. The 

 Eject "I these tests was to obtain a comparison with the 

 ordinary tensile tests. The results showed that, on the 

 average, the bursting tests on parallel doubled rubbered 

 cotton gave results a little higher than the tension test, 

 while for diagonally doubled fabrics the mean of the burst- 

 ing tests was about ii times as great as the tension test. 

 For single oilskin the bursting test gave a slightly lower 

 figure than the tensile. 



tearing Tests. — Some tests have been made to determine 

 the effect ot a small wound in the fabric on its strength, 

 with the view of indicating, if possible, the factor of salety 

 necessary to ensure that such a wound or tear shall not 

 immediately spread. The disturbance of stress distribution 

 caused by such a wound is accommodated within a large 

 but finite area of the fabric, which may be called the 

 " danger rectangle." It was expected that the applied 

 stress causing rupture of a specimen containing a relatively 

 small cut of fixed magnitude would be independent of the 

 dimensions of the specimen provided it were at least as 

 large as the " danger rectangle," and the results obtained 

 were in agreement with this theory. The necessary factor 

 of safety for wounds of different sizes was given, for the 

 particular fabric tested, as the result of these experiments. 

 The work was limited to wounds of small size, which 

 would, however, include ordinary bullet holes ; apparatus is 

 under construction to enable the work to be extended to 

 wounds of larger dimensions. 



Permeability Tests. — A large number of rubbered and 

 other fabrics have now been tested for permeability by 

 hydrogen. The apparatus employed continues to give satis- 

 factory results, which can be relied upon to a high degree 

 of accuracy. The practical conclusions to be drawn from 

 these tests, especially when considered in conjunction with 

 the weathering tests, would appear to be of considerable 

 importance. 



In the case of rubbered fabrics, the permeability is found 

 to be more or less directly dependent on the quantity of 

 rubber employed ; the lighter rubbered materials show a 

 higher permeability, a number of samples tested exceeding 

 the maximum of 10 litres per square metre per twenty-four 

 hours usually allowed in French specifications. This is 

 especially the case with the parallel doubled cloths 

 examined, and the work done points to the superiority of 

 diagonal doubling from this point of view. The permea- 

 bility of rubbered fabrics increases rapidly with rise of 

 temperature, the increase being as much as 9 per cent, 

 per degree centigrade in the samples tested. 



Samples of oilskin, varnished silk, and of other fabrics 

 proofed in various ways have also been tested for permea- 

 bility. The exact nature of the proofing is not in all cases 

 known. Some of these have shown excellent qualities as 

 regards their hydrogen-holding capacity, the permeability in 

 many of the samples being less than 1 litre per square 

 metre per twenty-four hours, and in some instances not 

 exi eding a quarter of this amount, with a less weight 

 than that of the lighter rubbered fabrics above referred to. 

 In some of these fabrics the hydrogen-holding capacity 

 appeared to improve with rise of temperature. 



Tests have also been made on a number of samples with 

 joins. In the rubbered fabrics tested, and in some of the 

 others, the permeability of the join was no higher than 

 that of the rest of the fabric, but with proofing other than 

 rubber the join has sometimes been found to have a much 

 higher permeability. This is a point, therefore, to which 

 attention must be paid. The joins have also sometimes 

 shown a deficiency in tensile strength. 



Weathering Tests. — The weathering tests of fabrics have 

 been directed to the determination of the rate of loss of 

 tensile strength and the rate of increase of permeability due 

 to exposure in the open. The rate of diminution in tensile 

 strength does not show any very important difference 

 NO. 2176, VOL. 8"] 



between the rubbered fabrics tested and those proofed in 

 other ways. It is of interest, however, to note that the 

 rate of deterioration was usually found to be most marked 

 during the second month of exposure. Thus for one fabric 

 the losses in strength in the first three months of ex- 

 posure were approximately 9, 28, and 10 per cent., and 

 similar figures have been obtained for other fabrics. 



As regards the effect of exposure on permeability, the 

 difference between the rubbered fabrics tested and some of 

 the fabrics proofed in other ways has been very marked. 

 In unprotected rubbered fabrics the deterioration in 

 hydrogen-containing capacity has usually been compara- 

 tively rapid. The effect of the usual yellow protective 

 colouring is, however, considerable. In several uncoloured 

 samples, after fifty days' exposure in the open, the 

 hydrogen leakage has been found to exceed 100 litres per 

 square metre per twenty-four hours. A number of yellow 

 fabrics, however, which have been exposed for some five 

 or six months, are still moderately gas-tight, and, further, 

 as regards tensile strength, are only a little weaker than 

 the unexposed samples. From the more recent tests it 

 appears that sunlight is the most important factor in pro- 

 ducing deterioration. 



On the other hand, the oilskins, varnished silk, &c„ 

 tested have not, in general, shown any appreciable increase 

 in permeability with exposure. If taken down for test on 

 a warm day, their hydrogen-holding capacity has often been 

 found to have improved. In some cases where a sample 

 has shown deterioration, it has again improved after further 

 exposure, the temporary increase in permeability being 

 probably due to crumpling when cold. 



A very complete scheme of tests on rubbered and other 

 fabrics is now in progress to examine more closely the 

 rate of deterioration with exposure, and to distinguish 

 between the relative effects of sun and moisture. Tests of 

 various proofing materials are also being carried out at 

 the laboratory, and some satisfactory results have been 

 obtained. 



Light Alloys. — A considerable amount of experimental 

 work has been carried out on light alloys intended for 

 structural work on airships and aeroplanes. Samples of 

 the allov known as " duralumin " have been supplied by 

 Messrs. Vickers, Ltd., and the mechanical tests made on 

 these were in general agreement with the results found at 

 Barrow. Samples of channel bar tested at the National 

 Physical Laboratory gave a tensile strength of 257 tons 

 per square inch, and samples of wire 30 tons. Further 

 investigation of this alloy will be undertaken, including 

 ageing^ fatigue, and corrosion tests, special attention being 

 paid to the question of the perrrranence of the material. 

 Tests of this kind are being made by the metallurgy 

 department in conjunction with similar work on light 

 alloys prepared in the laboratory. Some of these, at pre- 

 sent being studied in connection with the work for the 

 Alloys Research Cpmmittee of the Institution of Mechanical 

 Engineers, are showing very promising results, tensile 

 strengths up to 34 tons per square, inch having _ been 

 obtained, together with reasonable ductility and without 

 recourse to special thermal treatment. When these new 

 allovs have been more fully studied it is hoped that some 

 of them will prove of service for aeronautical construction. 



Meteorological Work. — The preliminary programme of 

 experimental work adopted by the committee upon their 

 appointment included the following items : — 



(32) General information relating to the variation of 

 wind velocity and phenomena connected with gusts of 

 wind. 



(33) Relative variation in speed and direction of the wind 

 at different heights above the earth's surface. 



(34) Vertical movements in the air. 



(35) Rotary movements in the air. 



(36) Electrical phenomena. 



(37) Formation of clouds, snow, hail, &c. 



The items numbered (32) to (35) were dealt with pro- 

 visionally in a memorandum on details of wind structure, 

 &-c, by "Dr. Shaw, presented with the report of the com- 

 mittee' for last year. This has been followed up by further 

 experimental work on vertical motion and rotary motion 

 in the atmosphere at Pyrton Hill, by Mr. J. S. Dines, 

 under the direction of the Meteorological Office. The 

 results of the investigation are presented by tliree 

 memoranda included in the technical report. 



