NA rURE 



[August 2, 1906 



text-books on the subject (e.g. Rosenbusch's " Microscopical 

 Physiography ") as being cut " so that one of its faces is 

 exactly parallel to the principal axis (optic axis, axis of 

 least elasticity)." The difficulty in getting, say, iron-grey 

 of the first order depends on the extreme thinness of the 

 quartz required at the thin end of the wedge. 



Now the interference colour given by plates of equal 

 thickness of the same mineral depends on the direction in 

 which they are cut, varying from a maximum when the 

 plate is parallel to the optic axis to zero when the plate 

 is perpendicular to that direction (assuming the mineral 

 to be uniaxial). If, then, a wedge be made having one face 

 parallel to some such direction as, say, an r or s face of 

 the quartz crysta' and its length in the direction of the 

 trace of the vertical plane of symmetry through that face, 

 it will give the same results as the ordinary quartz wedge, 

 but, for the same thickness, will give a lower colour, so 

 that the colours at its thin end may be got very low. On 

 trial a wedge made in this way gave very satisfactory 

 results. 



The compound wedge described below, which, so far as 

 I know, is also new, was found to be still better. Suppose 

 a sheet of muscovite be taken, its axes of elasticity deter- 

 mined, and a strip cut of the same size and shape as the 

 quartz wedge with the axis of greatest elasticity parallel 

 to its greatest length. If the wedge is covered with the 

 mica plate and examined between crossed Nicols, there 

 will, of course, be a black compensation band in some posi- 

 tion, and by cleaving the mica thinner this band can be 

 made to move towards the thin end of the wedge, and 

 finally to coincide with it. The mica is now cemented to 

 the quartz, and a wedge is produced which gives all the 

 colours of the first order. By the use of this compensation 

 mica plate a very poor wedge may be converted into a first- 

 class instrument, or one broken at its thin end restored to 

 usefulness. Daniel James Mahony. 



The Grand Hotel, Melbourne, Victoria, June 25. 



Colour Phenomena in "Boletus ccerulescens." 



One day recently in the woods at Lynton (where the 

 soil is red) I found and gathered two very beautiful toad- 

 stools, with vermilion stem and bright, sulphur-coloured 

 hymenium. In these individuals the striking colour pheno- 

 mena peculiar to their family were remarkably in evidence; 

 in the brilliant sunlight on the bright yellow under-surface 

 of the pileus I found my name when traced in the most 

 gentle way shine out almost immediately in the most 

 magnificent of blues. 



Will any of your readers kindly refer me to any recent 

 papers concerning the chemical or physical processes which 

 underlie this fascinating demonstration? From my own 

 superficial observations it is evident, I think, that light 

 plays an important part. The energy liberated by the very 

 gentlest friction appears to be a sufficient initiative. 



Parts that have been rendered blue, when left at rest, 

 after a short time return to yellowness, but these same 

 parts are capable under fresh stimulus, so long as the 

 fungus is still alive, of again assuming temporary blue- 

 ness. 



The juice expressed from blue areas is itself bright blue, 

 and imparts a bright blue stain to linen. Upon my hand- 

 kerchief this colour remained so long (at least five hours) 

 that I thought I had fixed it ; but in the morning the dry 

 blue patch of the night before was no longer blue, but 

 yellow. 



On cutting the stem its upper two-thirds was found 

 endowed with the property of coerulescence ; but this was 

 not in any degree possessed by its lower third, in which 

 the cut surfaces remained of a reddish-brown colour. With 

 the exception of the lower part of the stem and the cuticle, 

 all the tissues of the fungus exhibited ccerulescence. 



I take special interest in these observations on account 

 of certain phenomena noticeable in human tissues in the 

 course of a somewhat rarely met with pathological condition 

 which has been described under the name chloroma. 



Without entering into details, I may remark that along 

 with the colour development which characterises this patho- 

 logical condition hsemoglobin is probably being extensively 



NO. I918, VOL. 74] 



set free from red blood cells, and presumably this body 

 or its derivatives are abnormally abundant in the body 

 fluids. Is there any known organic iron-containing body 

 capable of being responsible for these quick-change effects? 

 Edgar Trevithick. 



Strength of a Beetle. 



Last night a small beetle (Aphoditis fossor), the length 

 of which is i inch, flew in at my window and alighted 

 on a table next to me. As it buzzed about I put a lid of 

 a tin box over it, but to my surprise the beetle walked 

 about bearing the lid on its back. I then put the tin box 

 on the top of the lid, and was absolutely amazed to find 

 that the insect tilled up a corner of the combined box and 

 lid, and nearly escaped. The weight of the beetle when 

 dead was i grain, alive I suppose it was a little more ; 

 but the box and lid weighed 175S grains ! Assuming that 

 the living insect weighed i grain, it must have tilted up 

 1758 times its own weight ! Of course, the strength re- 

 quired to tilt up a box on edge is nothing like so great as 

 that required actually to lift the weight, but nevertheless 

 the feat seems to me sufficiently astounding. The 

 dimensions of the box are 3jX2|x iJ inches. 



Charles R. Keyser. 



The Gables, Hay ward's Heath, July 26. 



THE INTERNATIONAL CELEBRATION OF 

 THE JUBILEE OF THE COAL-TAR IN- 

 DUSTRY. 

 TOURING the last century no discovery, perhaps, 

 ^-^ has led to such far-reaching and important de- 

 velopments as that of mauve, the first aniline dye, by 

 William Henry Perkin. Not only was the door 

 thrown open to the never-ending procession of 

 artificial colouring matters, but the raw materials 

 necessary for their production were also the raw- 

 materials for the synthesis of whole series of entirely 

 different substances, which have now assumed most 

 important positions in the world's daily requirements. 

 It cannot be too often repeated that Perkin 's dis- 

 covery was the result of true scientific devotion to 

 pure research. The S3mthetic preparation of quinine 

 was the goal aimed at — a sufficiently ambitious one 

 for a lad of seventeen, for the problem is yet unsolved. 

 Perkin did not state, as is perhaps too often done 

 nowadays, that "only a black mass was obtained." 

 His persevering and scientific habit of mind led him 

 to investigate the "black mass," with the result that 

 by extraction with alcohol was isolated the violet dye 

 which is so closely associated with his name. 



Great though Perkin 's discovery was, yet greater 

 still were the zeal, industry, and genius of the boy of 

 eighteen which enabled him to make the dyestuff on 

 the large scale and place it on the market success- 

 fully. Only those who have had experience in lange- 

 scale preparations can realise what this must have 

 meant. New plant, new materials, new conditions : 

 all had to be undertaken, and in the introduction of 

 iron vessels for the manufacture of his raw material, 

 aniline, Perkin laid the vast aniline oil industry under 

 lasting obligation. 



The start thus given, many entered the field; by 

 a slight variation of Perkin 's process Renard 

 and Franc introduced the splendid crimson dye 

 " magenta " in France, whilst shortly afterwards 

 Simpson, Maule, and Nicholson started the manu- 

 facture of this colour in London. The happy collabor- 

 ation of A. W. Hofmann, the college professor, with 

 the splendid technical chemist and business man, 

 E. C. Nicholson, soon not only placed the London 

 firm in a commanding position, but gave to the world 

 those researches on rosaniline for which Hofmann 

 became so famous. 



