July 15, 1920] 



NATURE 



613 



controversy with Mrs. Ayrton. It will suffice to say 

 that she is writing of things of which her kniowledge 

 is, naturally, second-hand, besides being clearly very 

 inadequate. This is apparent in at least eight separate 

 points in her letter, of which I will only refer to her 

 mention of the successful use of the fans in what 

 must obviously have been a very exceptional type of 

 " mustard-gas " bombardment. 1 assure Mrs. Ayrton 

 that she is mistaken if she imagines that she has in 

 this matter any considerable body of support amongst 

 those who^knew the facts, from whatever point of 

 view. I hope, in conclusion, that nothing I wrote has 

 led Mrs. Ayrton to suppose that I regard her advocacy 

 of her fans to be influenced by questions of "payment 

 or reward." Nothing was further from my mind. 



A. J. Allmand. 

 King's College, W.C.2, June 30. 



Prof. Allmand, having read neither the specific 

 charges I have made against the War Office nor the 

 evidence, principally from official documents, with 

 which I have sustained them, attempts to counter 

 them with statements unsupported by evidence of any 

 kind. He finds me ignorant, for instance, on eight 

 points, of which the only one he names is obviously 

 no matter either of my knowledge or ignorance, since 

 it refers simplv to a quotation from the letter of a 

 very able and gallant "fighting- soldier." Had he 

 read the article he criticises he would have seen the 

 whole quotation. 



I am ready to sustain those charges, and to produce 

 the evidence before any proper tribunal. I repeat 

 them. 



I accuse the War Office of having caused great loss 

 of life and much avoidable suffering by : 



(i) Having refused for a whole year to make use 

 of anti-gas fans, which they were yet compelled 

 finally to adopt owing to their proved efficacy. 



(2) Never having" set up an efficient organisation 

 for training officers and men in their use, although 

 I had warned them that this was indispensable. 



(3) Having thus deprived the troops of the know- 

 ledge requisite for understanding what could be donfe 

 with the fans, and having thereby induced the idea 

 that they were useless. 



(4) Having trusted entirely to fires for clearing dug- 

 outs of gas, regardless of the fact that in many places 

 drv wood and paper were often unobtainable. 



(5) Ranking sandbags and ground-sheets as of equal 

 efficacy with fans for clearing gas. 



(6) Sending out an inadequate supply. 



The scientific men implicated in these grave charges 

 have not even made the plain statement with regard 

 to them that the Editor of Nature considered so 

 desirable, much less produced any evidence in refuta- 

 tion of them. Hertha Ayrton. 



July ir. 



The continuance of this correspondence in our 

 columns would not, we think, serve any useful pur- 

 pose. In a note in Nature of May 13 it was pointed 

 out that Mrs. Ayrton 's indictment of the War Office 

 was " not against the military element, but rather 

 against the experts who were associated with the Gas 

 Service." It is easy to understand the reluctance of 

 these officers to express their views upon anti-gas 

 fans, even if thev were free to do so; and though 

 Mrs. .Avrton is anxious to have all the facts judged 

 by a tribunal appointed for that purpose, we must 

 confess that the likelihood of a scientific bodv con- 

 stituting such a tribunal is verv remote. The inquiry 

 is one that the Conjoint Board of Scientific .Societies 

 could take up appronriatelv. but no satisfactory con- 

 clusion could be reached without examining a number 

 of witnesses, and the resources and powers of the 

 NO. 2646, VOL. I05I 



Board are scarcely sufficient for such action. The only 

 practicable course, therefore, would seem to be for the 

 War Office to appoint a Committee to investigate 

 Mrs. Ayrton 's charges, and in the interests of scientific 

 truth and efficiency we hope this will be done. — Ed. 

 Nature. 



The Stretching of Rubber in Free Balloons. 



In Nature of June 10, p. 454, in connection with 

 the attainment of high levels of the atmosphere by 

 sounding- or pilot-balloons, Mr. VV. H. Dines con- 

 siders that such balloons would burst before reaching 

 great heights, as the rubber of which these balloons 

 are made would be stretched eightfold linearly, and 

 he remarks that he does not think that any rubber 

 will stand this treatment. 



Properly vulcanised soft rubber will, however, 

 stretch to more than ten times its original length if 

 in the form of a ring-shaped test-piece. Moreover, 

 the load increases more rapidly than the elongation 

 at the later stages. The remarkable tensile properties 

 of soft rubber are not always sufficiently recognised. 

 The breaking strain of a properly vulcanised sample 

 should be not less than 1500 grams per sq. mm. cross- 

 sectional area of the original test-piece. Allowing 

 for the stretching, which would reduce the cross- 

 sectional area to one-tenth, the breaking strain would 

 be 15,000 grams f>er sq. mm. cross-sectional area of 

 the sample when fully elongated, or nearly 10 tons per 

 sq. in. It would not, however, be safe to rely on these 

 figures, as the rubber of the balloon would tear at the 

 neck where it is tied together before the bursting pres- 

 sure was reached. Mr. Dines has also failed to take 

 into consideration the fact that part of the hydrogen 

 would be lost by diffusion during the ascent of the 

 balloon, which would reduce the pressure of the con- 

 tained gas. Henry P. Stevens. 



15 Borough High Street, London 

 Bridge, S.E.i, June 29. 



With reference to Mr. Stevens's interesting state- 

 ments about the stretching of rubber, I think he has 

 overlooked the fact that in a balloon the rubber is 

 stretched simultaneously in both directions, whereas 

 he refers apparently to one direction only. 



I have cut a strip half an inch wide from a balloon 

 used at Benson ; it stretched sevenfold before break- 

 ing, but when extended sixfold its width was reduced 

 from 0-50 in. to 0-22 in., instead of being extended 

 to 3-00 in., as would be the case in actual use. Its 

 unstretched thickness was 0-013 in., its thickness at 

 breaking greater than 0-004 in., but when extended 

 sixfold each way its thickness would only be 

 0-00036 in. 



The loss of hydrogen by diffusion or leakage is 

 equivalent to not giving the balloon so large a free 

 lift at starting, and would alone increase the height, 

 but in practice it sometimes leads to the bursting 

 height not being reached at all because the free lift 

 Tias vanished before that point is reached. It has 

 been found that within fairlv wide limits the maxi- 

 mum height is only slightly dependent on the free lift 

 at starting. But diffusion of the hvdrogen outwards 

 is ^accompanied by diffusion of air inwards, and this 

 increases the specific gravity of the gas and lessens 

 the height. 



I did not mention the effect of the tension of the 

 rubber on the pressure, and therefore on the specific 

 gravity, of the enclosed gas. Taking Mr. Stevens's 

 figure of a breaking strain of 15,000 grams per 

 sq. mm. of unstretched section, this will raise the 

 internal pressure by quite an appreciable amount, and 

 thereby reduce the height at which the balloon bursts,, 



Benson. W. H. Dines. 



