November 25, 1920J 



NATURE 



409 



but mere conservatism that makes us hesitate to 

 abandon all of it, and lO admit that, even in respect 

 of energy, a fixed electron can have the properties 

 which classical dynamics attributes to a moving 

 electron? Classical dynamics, it is clear, is only 

 ■■ statistical " ; what are the principles of the elements 

 of the statistical group is the main problem of the 

 physics of the future. Norman R. Campbfxl. 



November i6. 



The Testing of Balloon Fabrics. 



On p. 130 of the Report of the National Physical 

 Laboratory for 1919 reference is made to the testing 

 and experimental work carried out in connection with 

 the manufacture of balloon fabrics for war purposes, 

 and in connection with this we wish to place on 

 record this company's work in the manufacture of 

 materials, especially hydrogen-proof fabric, for 

 lighter-lhan-air craft. 



The North British Rubber Co., Ltd., first took up 

 the manufacture of this material in 1908, and, 

 realisinc that the problems involved in manufacture 

 necessitated scientific control, as a preliminary in- 

 stalled in its laboratory an apparatus for measuring 

 the porme.-ibilitv of rubber to hydrogen, and there- 

 after initiated research into the factors responsible 

 for the deterioration of rubber under the influence of 

 light. 



When the .Admiralty installed its test station at 

 Manchester we were requested bv the oflficer in charge 

 to furnish drawings of the special type of hydrogen 

 diffusion apparatus which had been designed at Castle 

 Mills, and one of its staff received a course of 

 mstruction in the company's laboratories on the pro- 

 cedure to be followed in testing balloon fabric. .At 

 a later period of the war this department was taken 

 over by the newly formed War OflTice .Aircraft Fabrics 

 Oenartment, which installed an extended testing plant, 

 and another member of that staff also received his 

 training in this work in our aeronautical labora- 

 tories. 



The Aeronautical Inspection Department was also 

 indebted to the laboratory of the North British Rubber 

 Co., I,td., for the training of some of its scientific 

 staff, and its testing equipment was in many 

 respects also based on the results of this experience. 



During the course of the war our output was 

 steadily increased, and at the armistice we were 

 manufacturing more than 35.000 vards of balloon 

 fabric per week, every piece of which was tested in 

 our aeronautical laboratories for weight, strength, 

 and hydrogen leakage. 



The investigation of the research laboratory into 

 the action of licht on rubber resulted, moreover, 

 amongst other thint's, in a discovery which, without 

 any increase in weight, permitle<l the production of a 

 fabric of vastly enhanced durability specially suitable 

 for use in the tropical theatre of the war. 



Our reason for asking for the publication of this 

 communication is only for the purj ose of stating that at 

 least one manufacturer was sufficlenllv well equipped, 

 not only in the manufacture, but also in their scientific 

 M.-iff and laboratories, to carry on without outside 

 help, and it is not intended to detract in any wav 

 from the very useful and great assistance which the 

 National Physical Laboratory gave to Government 

 n<pnrtments and others starting out in what was 

 [irr,l>,Tblv new ground to them. 



W. A. Wll.l.lAMS, 



Works Manager. 

 I he North BrifiKh Riibb"r Co.. I,td., Castle 

 Mills, I'.cllnhurnh, Nnvenibrr 12. 

 NO. 2665, VOL. 106] ' 



Luminosity by Attrition. 



With reference to Sir Ray Lankester 's suggestion in 

 Nature of November 4 that chemists should endeavour 

 to ascertain the cause of the " empyreumatic " odour 

 which accompanies the flashes of light produced by 

 rubbing two quartz pebbles together, may 1 suggest 

 also that the inquiry might be extended to include 

 other substances which possess this property of tribo- 

 luminescence ? 



The property is not confined to crystallised silica; 

 it is displayed also by the amorphous varieties (opal, 

 etc.) and by flint and'chert. 



Felspars possess the property in varying degrees ; in 

 general, it is more pronounced in the alkali felspars 

 than in the lime-soda species. Fused albite displays 

 the property. 



Certain types of igneous rocks, both crystalline and 

 glassy, behave in the same way. The property is 

 most marked in the acid types; in the basic types 

 (e.g. picrites, etc.) it is feeble or wanting. 



Among the sedimentaries, sandstones, arkose, etc., 

 and among the metamorphics, gneiss and some 

 crystalline schists, display the property. The em- 

 pyreumatic odour is a general accompaniment in the 

 cases referred to above. 



Saccharin and certain varieties of sugar possess the 

 property in a moderate degree, and Dr. Lawson (New- 

 castle) has observed it in uranium nitrate when 

 crystals of the salt are shaken up in a bottle. 



I have investigated a large number of other sub- 

 stances_ (artificial glasses, rocks, and minerals); in 

 the main, the results are negative. 



Luminescence occurs between any pair of the 

 " active " rock or mineral substances mentioned, and 

 it would seem that the property is not dependent on 

 crystallinity or wholly on chemical composition, but 

 its relation to silica content (in silicates, etc.) is as 

 yet obscure. 



As regards the crystalline substances, the idea preva- 

 lent on the Continent is that during the process of 

 crystallisation some of the outer electrons of the atotn. 

 system become detached, as it were, from the rest, 

 but can recombine, with accompanying luminescence, 

 under the stimulus of violent vibration. On the other 

 hand, it may be a piezo-electric phenomenon; strain 

 and deformation may induce positive ami negative 

 electrical charges on neighbouring particles, discharge 

 bcintj accompanied by luminescence. As the inves- 

 tiijation is incomplete, further discussion would be 

 out of place. A. Bramuaix. 



Imperial College of Science and Technology 

 (Royal School of Mines). South Kensing- 

 ton, S.W.7, November 13. 



Spiranthei autumnalia. 



In Natikf of September i(), p. 70, I refwrtf-d the 

 occurrence of this orchis, new to Scotland, in Lower 

 Strathspey. As I can find no record of the species 

 growing on soil other than cretaceous, and as there 

 in no lime in the .soil where I found the plants, 1 

 suspect that I may have been deceived by the super- 

 ficial resemblance between Spiranthes and Ooodyera 

 ref>en<!. The noint, of course, mipht have been decktod 

 at once by lifilng a root; but, being very unwilling to 

 disturb rare plants, I refrained from doing so. I 

 hope to return to tlic place next summer to verify the 

 species; until then I must ask botanists to dismiss 

 my note as non avenue. If it should prove that I 

 have erre<I. I have done so in good company, for wa» 

 not Sir Joseph Hool<er deceived by the decussate, 

 scale-like Icayes of Veronica cupreiaoides into pro- 

 nouncing that plant 10 be coniferous from specimens 

 sent from Ni-w Zealand? IIrrrf.kt Maxwrii.. 



Monreilh 



