NATURE 



[February 2, 1899 



than under the cover of anonymity. His Grace will, I trust, 

 extend to me at least a small measure of " intellectual in- 

 tegrity " on that score. If the "experts" are to be weighed 

 and measured by some standard of the Duke's creation, then it 

 is obvious that this body of gleaners might reasonably expiess 

 some kind of opinion as to the value of the treatment to which 

 their facts are being submitted. I have already endeavoured to 

 put forward a plea on behalf of the non-expert philosophical 

 writer, and I have expressly said that naturalists will ascertain 

 for themselves the credentials of each svriter. The Duke's 

 contributions have for many years been of a purely destructive 

 order ; how far the credentials of a writer who has contributed 

 .so little constructively to the edifice of biological science will 

 carry weight with the body of working naturalists is for them to 

 declare. 



A few words in conclusion as regards the electric organs of 

 the torpedo. I am the last person to ignore the difficulties in 

 the way of the theory of natural selection. Perhaps I have 

 more faith than my late lamented friend Dr. Romanes in the 

 power of a theory which explains so much being able, when we 

 know more about them, to meet such cases as these ; but this is 

 a purely personal matter. The particular difliculty in question, 

 like most others of weight, was long ago suggested to Darwin 

 himself, and was discussed in the " Origin of Species" (6th ed., 

 p. 150). It was discussed also in a letter to Lyell in i860 

 (" Life and Letters," vol. ii. p. 352). But if the whole theory 

 of natural selection were to break down on such a difliculty, the 

 doctrine of a "preconceived plan " would not help us in the 

 least. It would not be a philosophical explanation, but, with 

 the very greatest deference to my noble antagonist, a pseudo- 

 philosophical explanation, and, as such, I have felt, and always 

 shall feel, it my bounden duty to science to w'arn the public 

 from attaching any serious importance to it. R. Mei.doi..^. 



The British Museum Catalogue of Birds. 



Mv attention has been drawn to some inaccuracy (no doubt 

 unintentional) in the historical account of the production of the 

 Catalogue of Birds given in a recent number of Nature. Will 

 you, therefore, kindly allow me to correct that account ? 



At the time of Mr. Bowdler Sharpe's appointment (September 

 1872) to an assistantship in the Zoological Department of the 

 British Museum, the Keeper of the Department, Dr. Gray, was 

 in so feeble a state of health (consequent on a paralytic stroke) 

 that the administration of the Department had devolved upon 

 Dr. Giinther holding the post of assistant-keeper. Inuring the 

 preceding period of his assistant -keeper.ship, Dr. (Uinther had 

 gone through the whole collection of birds, and formed the 

 opinion that a descriptive catalogue on the lines of his own 

 Catalogue of Fishes ought to be prepared for publication. With 

 this object in view Dr. Giinther recommended to the Trustees 

 the appointment of Mr. .Sharpe, who, on account of his enthu- 

 siasm, energy and general ornithological knowledge, seemed to 

 be specially qualified to undertake the catalogue. Dr. Gray 

 gave his ready consent to the preparation of the catalogue, 

 and the Trustees sanctioned the publication when the MS. of 

 the first volume was laid before them in 1874. Thus, although 

 it is the fact that the preface to the first volume was signed by 

 Dr. J. E. Gray, yet the plan of the work was initiated and 

 elaborated by Dr. Giinther, and the work was, during its pro- 

 gress, kept under his constant supervision. 



I:',. R.w Lankestkr. 

 Director of the Natural History Departments 



February i. of the British Museum. 



Queries on the Reduction of Andrews' Measurements 

 on Carbonic Acid. 

 To begin with, let me quote a few passages from Andrews' 

 paper. On pp. 301-302 of his "Scientific Papers" he says : 

 " I have not altempte<l to deduce the actual pressure from the 

 observed changes in the volume of the air in the air-tube. For 

 this purpose it would be necessary to know with precision the 

 deviations from the law of Mariolte exhibited by atmospheric 

 air within the range of pressure employed in these experiments. 

 ... It will be easy to apply hereafter the corrections for true 

 pressure when they are ascertained, and for the purposes of this 

 paper they are not required. The general form of the curves 

 representing the changes of volume in carbonic acid will hardly 

 undergo any sensible change from the irregularities in the air- 



NO. 1527, VOL. 59] 



tube ; nor will any of the general conclusions at which I have 

 arrived be affected by them. It must, however, always be 

 under-stood that, when the pressures are occasionally spoken of, 

 as indicated by the apparent contraction of the air in the air- 

 gauge, the approximate pressures only arc meant." 



In every one of his papers specially devoted to the subject he 

 was careful to mention the fact that he was unable to give the 

 true pressures which correspond to the indications of the air- or 

 hydrogen-manometer. The question seems to have hung con- 

 stantly upon the mind of the experimentalist in the course of 

 his investigations. In spite of this, however, the values of 

 pressure given by him have often been treated as if they were the 

 true values, and in the discussions of the characteristic equation 

 of carbonic acid, agreement or disagreement to within I, 10 of an 

 atmosphere is spoken of. But according to .\magat's measure- 

 ments on air, hydrogen, or nitrogen, the corrections to be 

 applied are quite large. 



In a paper in the Philosophical Magazine, vol. xxiii., fifth 

 series, Ramsay and Voung have tried, on the basis of .\ndrews' 

 experiments, to show that in the ca.se of carbonic acid there 

 holds good very approximately the constant volume relation that 

 the pressure under this condition varies linearly as the tempera- 

 ture. They state that they have reduced to absolute units, 

 as far as possible, the values of pressure given by Andrews by 

 means of -Vmagat's experiments on air. These latter experi- 

 ments were made at 16 , while the temperature of Andrews' 

 manometer varied within a considerable range, from 5° to 15°. 

 Is the influence of temperature on the manomelric correction 

 negligible when the pressure is high ? I can show in the case 

 of nitrogen, on the basis of Amagat's experiments, that this 

 auxiliary correction due to temperature variation is generally 

 quite large, sometimes of the same order of magnitude as the 

 main correction itself; and it seems very improbable that in this 

 respect air would difl^er very much from nitrogen. 



The same remark applies to the calculations of Margules 

 (IVieii. Sifz/ieih., xcvn. 2a, 1888), and also to my calculations 

 relating to Andrews' measurements on the mixtures of nitrogen 

 and carbonic acid {/'hi/. Mag., vol. xxxvi. 5th series). 



.■\nother point which has for a long time remained a query to 

 me, is the level dift'erence of the mercurial columns in the air 

 and carbonic acid tubes. Let me again quote from Andrews' 

 paper. On p. 303 of his "Scientific Papers" he says: 

 " ilaving thus ascertained the volumes of the air and of the 

 carbonic acid before compression, at o' and 760 millims. , 

 it was ea.sy to calculate their volumes, under the same 

 pressure of 760 millims., at the temperatures at which 

 the measurements were made when the gases were com- 

 pressed, and thence to deduce the values of the fractions 

 representing the diminution of volume. But the fractions 

 thus obtained would not give results directly comparable for 

 air and carbonic acid, .-\lthough the capillary glass tubes in 

 the apparatus communicated with the same reservoir, the 

 pressure on the contained gases was not quite equal, in conse- 

 quence of the mercurial columns, which ccMifiried the air .and 

 carbonic .acid, being of different heights. The column always 

 stood higher in the carbonic-acid-tube than in the air-tube, so 

 that the pressure in the latter was a little greater than in the 

 former. The dilTerence in the lengths of the mercurial columns 

 rarely exceeded 2co millims., or about one-fourth of an atmo- 

 sphere. This correction was always applied, as was also a 

 trifling correction of 7 millims. for a difierence of capillaiy 

 depression in the two tubes." In another pLice (p. 422) he 

 says : " The pressure in atmospheres, as indicated by the air- 

 manometer, on the gas in the carbonicacid-lube was given by 

 the e<)uation 



V„(..K./) ,/ 



^ V, ^760' 



in which V,, is the volume of the air at o' and 760 millimetres, 

 \', the observed volume at the temperature /, and </ the differ- 

 ence of level (corrected when necessary for difference of capillary 

 depression) of the surface of the mercury in the manometer and 

 carbonic .acid tubes." 



Thus what is given as S or /» in .\ndrews' papers includes in 

 itself the level difference </, and what is really required in calcu- 

 lating the corresponding manometric correction is V, ; ./ is not 

 given in .Andrews' papers. The manomelric corrections, then, 

 which are based on the given values of / alone, will differ from 

 what they ought 10 be by something like \ of an atmosphere. 



Thus one will find himself prevented from entering upon a 



