Sept. 29, 1882.] 



♦ KNOWLEDGI£ <. 



It appears tliat another metachromatic scale has been devised 

 besides my own. The two scales arc not identical, however, nor 

 does the same meaning appear to be attached to both. Thus the 

 deviser of the scale to which I refer, writes : — " White (as being 

 the combination of all colours) concludes the scale at the limit of 

 expansion, and black (as an absence of light) at that of contrac- 

 tion."* This is the very opposite of anything I have ever taught 

 regarding metachromatism, and from the experimental evidence I 

 have already given, the reader will perceive that it is undoubtedly 

 a mistake. 



By spectroscopic examination, I have ascertained that the change 

 of colour in a body upon elevation of its temperature is due to 

 increased absorption of light towards the violet end of the spectrum. 

 A simple experiment suggests itself to me by which the reader may 

 demonstrate this point to his own satisfaction without the spectro- 

 scope. A borate of copper bead, as obtained in blow-pipe analysis, 

 is blue when cold and green when hot. Now a transparent yellow 

 substance generally absorbs the violet end of the spectrum as far as 

 the blue border of the green, according to the thickness of the 

 absorbing substance. Treacle is a body of this kind. Take the 

 blue bead and dip it in treacle. Upon taking it oat with a thin film 

 of treacle covering it, it aJ^pears green. In other words, covering 

 the bead with a thin film of a substance absorbing the light of the 

 violet end of the spectrum has the same effect, so far as its appear- 

 ance goes, as raising the temperature of the bead, and consequently 

 the latter operation increases the bead's absorption of the violet end 

 of the spectrum. 



As we have seen, this increase in the absorption of light to 

 which metachromatism is due, culminates in blackness, or what 

 would be termed spectroscopically continuous absorption. At the 

 other end of the scale, one would hare a continuous spectrum from 

 the absence of absorption, and between the two extremes, partial 

 absorption. In 187i Lookyer proposedf five orders of spectra, 

 ranging from the spectroscopic appearances of bodies at ordinary 

 temperatures to the emission spectra of high temperatures. I 

 regard his 3rd, 4th, and 5th orders as misplaced, and would sub- 

 stitute for them the orders I have placed opposite them in the 

 following comparison. The error has evidently arisen from a 

 mixed study of what I have termed transverse and structural 

 absorption effects. t 



ORDERS OP SPECTRA. 



After Lockyer. 



1st Order, Line spectra ■) 



2nd Order, Channelled-space > 

 spectra j 



3rd Order, Continuous absorp-l 

 tion at the blue end. I 



4th Order, Continuous absorp- 

 tion at the rod end.J 



5th Order, Uniqne continnons 

 absorption 



Class II. Absorptive. 



Metachro- 



Continuous absorption . . . Black. 



Partial absorption — ") Brown. 

 i.e., absorption at | Red. 

 the blue and rod I Orange, 

 ends, or at any in- f Yellow, 

 termediate part of I Green, 

 the spectrum J Blue. 



Continuous spectrum ...White. 



iLtntt& to tf)t etiitov. 



• opinionn of hit corregpondentt. 



\_The Editor does nothoht himself refponitiUe/oi 

 Se cannot undertake to return mtinutcripts or to > 

 communicationt thoidd be at short a> possible, coniistently Kith full and ( 



All Edit 

 all Easiness 

 street, W.C. 

 iulL^'Xy""""'' ^'"^""' ""' ^"'-Office Order, should le made payable to 



*,♦ All letters to the Editor Kill le Numbered. For eonvenienes ef refert-nee, 

 correspondents, Khen refernng to any letter, Kill oblige by mentioning its nuiiittr 

 and the page on Khich it appears. 



Space will not allow of my going into the theory of metachro- 

 matism, and I would add, in conclusion, that those readers who are 

 interested in its biological applications may consult the " Proceed- 

 ings of the British Association for 1877," pp. 100-1, and " Science 



Pop All *' vnl ; T^»^ 9K1 t:i\ 



ings 



for All," vol. i., pp. 251-50 



* Chemical Neics, Sept. 8, 1876, p. 109. 

 t " Proceedings of the Royal Society," Juno 11 

 J Phil. Mag. for December, 1876. 



Caotiok.— Beware of the Party offering limitations of the " B 

 and Big ■• J " Pen. Bold by all reopoctablo Stationers throughout I 



Also the Hindoo Pens, Diagonal Points, N09. 1, 2, and 3. Snmpic Doi «ith all 

 Iho kinds. Is. Id. by post. Patentees of pens and penholders, Moeniven S 

 < aileron, I'en-maliers to lier Majesty's Government. ODlces, 23, Blair-slreet, 

 Edinburgh. (Established 1770 



'* fehow me a man who makes no mistakes, and I will show you a man who has 

 done nothing." — Liebig. 



CONSUMPTION FROM STATS. 

 [57(;]— It appears to me that in his haste to denounce the editor 

 of Knowledge (5G0), E. H. has omitted to read, with any care, my 

 remarks of June 23 (431), which are the ostensible cause of his 

 letter. I was well aware that, according to statistics, consumption 

 was commoner among men than women, but I cannot see that I 

 say in that letter that stays produce lung disease directly in the 



What I said then, I say now, that they cause an external de- 

 formity, which many people, (E. H. probably among the number) 

 are not ashamed to admire, forgetting that the corresponding in- 

 ternal deformity, which they do not see, produces a state of things 

 incompatible with health and vigour, and that the children of 

 women in this lowered state of constitution are more likely (as in 

 the offspring of other deformed animals) to fall a prcv to consump- 

 tion and other diseases of that class which belong to feeble 

 constitutions. 



E. II. is partially right in what he says as to women being able 

 to breathe higher up than men, but that only holds good as long as 

 no exertion is made. Women engaged in hard work breathe much 

 as men do, and I should like to see a woman walk up a hill, or run 

 upstairs, without re^uirtiii; the full use of her lungs. They do not 

 generally get it, but that is not to the point. 



What E. H. says about a particular state of health curing con- 

 sumption, on account of the difficullij of respiration, will probably 

 cause amusement to most of the readers of Knowleiige. The fact 

 as to the cure is so, but the reason is very different and too well 

 known to need repeating here j besides, not being a doctor, it is 

 hardly a subject the explanation of which I am qualified to enter 

 upon. 



Wo have not yet come fully to the end of the evil to the com- 

 munity oi' this .sy.sti'iii of "waists." It is only within the last 

 twenty y. ms il ti ^i:i\s liuve been cheap enough for all classes to 

 wear tlu m. ti 1 ; -,. of ten years old and upwards. Therefore, 

 till lat.ly iIm 11,1; I! \x.is constantly recruited by the cliildren of 

 mofliirs ulh M Ijuilii's were of the shape that nature ordained. 

 'riii- i^ iiMiv li.ingfast altered. Uow many jieople, for instance, 

 ill'' 1 li ■ 1 III tliat 28 to 30 inches would be the size of the waist 

 el :i Ih:i1iIi\ woman of medium height when left to nature? In 

 coiuiusion, miglit I suggest to E. U. to i-cad Mr. Tr6ves' "Dross 

 of tho Period," published by the National Health Society, 44, 

 Berners-street, and also a letter written by Dr. W. B. Carpenter, 

 in tho Echo of April 6 or 7, as he will there see what men who 

 undorstand anatomy and disease think of waists. 



P. W. II.4RBERTOX. 



THE TUBERCULOUS OR WARTY-SKINNED LIZARD. 

 {Ilelodcrma Horridutii.) 

 [577]— In reply to tho paper on the " Ilolodorm," in Knowledog 

 of Sept. 15, and in allusion to my own error in venturing a guess as 

 to the meaning of its name, permit me to offer a word. In announc- 

 ing tlio arrival of this venomous lizard in Land and H'aft'rof Aug. 6, 

 1 wrote: — " Conjecturally, A<i'o may have reference to the sunny 

 colour " ; because, while having been verbally informed that this 

 was the meaning of the word, I myself rather doubled it. Books 

 have subsequently proved bettor instructors, and, on comparing tho 



