440 



NATURE 



[December 2, 1920 



The decision on this point of the future of the 

 hif»her forestry training is a momentous one, since it 

 involves no less than the future correct management 

 of the majority of the forests of the Empire. 



E. P. Stebbing. 



University of Edinburgh, October 29. 



British Laboratory and Scientific Glassware. 



I HAVE read with much interest the letters in Nature 

 of November 4 from Prof. Bayliss and Mr. Frank 

 Wood on the subject of British glassware, and 1 

 think the whole truth lies, perhaps, between the two 

 opinions put forward. As a manufacturer of scientific 

 apparatus, and primarily of X-ray tubes, I have had 

 probably as trying an experience of glass as any manu- 

 facturer since 1914. 



it is well known, I presume, that prior to the war 

 the whole of the glass bulbs and tubing used in the 

 manufacture of X-ray tubes came from Germany, and 

 the quality was undoubtedly very fine indeed. Since 

 1914 we have been obliged to depend upon glass of 

 French, American, and English manufacture. 

 Although by no means without merit, the products 

 of the two first-named countries were discarded 

 directly the English makers were in a position to 

 give us anything at all adequate to work with, and 

 since 1916 I think we have not used any glass what- 

 ever other than that made in this country. 



Kt the present time the position is that a glass 

 reasonably good for our purpose is made by at least 

 two British firms. It works well in the flame and 

 preserves a good appearance, but it is impossible to 

 say that it has reached the high standard set by the 

 German product. So far as the purchasers of the 

 finished instrument are concerned they are not 

 affected, becau.se the imperfections of the British 

 glass, where they exist, manifest themselves during 

 the manufacture of the complete X-ray tube, and the 

 difficulties, therefore, are entirely connected with 

 manufacture, and not with the efficiency of the 

 working of the apparatus which is being constructed. 



It has seemed to me for a long time past to be a 

 matter for regret that the British manufacturers could 

 not make those small final improvements which would 

 give us exactiv the material we require instead of, 

 as at present, stopping a little short of the ideal. 



I believe there is no particular difficulty at the 

 moment in obtaining supplies of glass from Germany, 

 but up to now I have resisted every temptation to do 

 this, partlv on general sentimental grounds, but 

 largely because of the enormous amount of trouble 

 which has been taken by the two firms of which I 

 spoke in order to produce a glass suitable for X-ray 

 purposes. I am sure that from start to finish the 

 profit on this undertaking must have been negligible, 

 and there have been endless experiments and a very 

 large amount of waste, the cost of which has fallen 

 chiefly on the glass manufacturers themselves. 



For this reason I feel that every endeavour should 

 be made to place the British glassmakers in a position 

 whereby they could continue tc5 produce these special 

 glasses,^ the demand for which is comparatively small, 

 but which are, nevertheless, of the very greatest im- 

 portance to scientific workers in this country. Those 

 firms engaged in my particular branch of the electro- 

 medical industry are always only too ready to co- 

 operate in overv possible way with the glass houses 

 in order to secure in this country absolute independ- 

 ence in the matter of the supply of material. 



CUTHBERT .\NDRKWS. 



47 Red Lion Street, High Holbom, 



London, W.C.i, November 25. 



Heredity. 



In his letter to N.muke of November 25 Sir Archdall 

 Reid has ably stated some fundamencal biological 

 truths concerning heredity, and with many ot his 

 statements 1 believe all biologists would agree. From 

 the developmental point of view there is certainly a 

 sense in which all characters are alike, arising as the 

 result of the interplay of the germ and its environ- 

 ment, nature and nurture. In this limited sense it 

 is doubtless beside the mark to inquire whether nature 

 or nurture is more important, seeing that both are 

 es.sential elements in any development at all. From 

 this point of view it may be true, to cite Sir Arcfidall 

 Reid's example, that there is no fundamental differ- 

 ence between the head and the scar ; both may be in 

 one sense germinal, and in another acquired. 



But this does not go to the root of the matter, as 

 may be most readily pointed out by referring to the 

 latter part of the letter in Natlrk. Sir .Archdall Reid 

 says: "The sole antecedent of non-inheritance is 

 variation." The statement is true, of course, but he 

 goes on to assume tacitly that all variations are in 

 one category. Sir Archdall Reid recogni.ses the fact, 

 which Weismann emphasised, that "heritage travels 

 down the germ-tract," and draws the "necessary [his 

 italics] inference from this " that all characters of 

 the individual are " innate, acquired, and inheritable 

 in exactly the same sense and degree." But this is 

 surely a petitio principii, for while all inherited 

 characters ■ may come to travel down the germ-tract, 

 it does not follow that they all originated as 

 variations in the germ-tract. It is surely legitimate 

 to assume, until the contrary is proved, that new 

 characters may arise (to use ordinary biological 

 terms) as germinal variations or as impressed modi- 

 fications of the soma which are not represented in 

 the germ-tract. Indeed, this is the current distinction 

 drawn between mutations and fluctuations. In the 

 latter ca.se the question will arise whether the modified 

 soma may ultimately affect the germ-plasm ; in other 

 .words, whether a modification or an acquired 

 character may come to be inherited bv bringing about 

 an alteration in the germ-plasm. This is surelv a 

 legitimate inquiry. If so, it implies the possibility 

 that the " scar " miijht ultimately, having become 

 germinal, appear without the specific stimulus that 

 is now necessary to call it forth. 



R. RUGGLES G.ATES. 



King's College, Strand, W.C.2. 



NO. 2666, VOL. 106] 



The Mechanics of Solidity. 



Under this title Mr. J. Innes (N.wure, Novem- 

 ber 18) suggests, for the benefit of engineers, that 

 coefficients of thermal expansion are fairly closely 

 related to hardness. His list of thirty-eight materials 

 ranging from diamond to indiarubber is given in order 

 of thermal expansion. No definition of hardness is 

 suggested, and the figures, taken from three tables 

 of "hardness," are admittedly somewhat conflicting. 



Hardness, I take it, is due' in part to closeness of 

 atomic packing. Diamond, the hardest substance 

 known, possesses also the lowest known atomic 

 volume, while potassium, the softest element on Mr. 

 Innes's list, has by far the highest atomic volume, 

 i.e. has the loo.sest atomic packing. 



Diversities in hardness depend also on how far each 

 substance tested is removed from its melting point. 

 Taking fourteen elements from the list, and assuming 

 tests for hardness were made at uniform temperature, 

 the order of degree-distance below melting point comes 

 out : — Diamond, iridium, platinum, iron, gold, copper, 

 silver, aluminium, arsenic, antimony, lead, tin, bis- 

 muth, and sulphur. 



