April 21, 1892] 



NATURE 



581 



shown fail to recognize the bird at all. They speak also 

 of another flightless bird by the name of Mehunui. This 

 bird, one old and very intelligent Moriori informed me, was the 

 same as the Maoris called Kakapo. Mr. Alexander Shand, 

 an old resident in the Chatham Islands, and the sole European 

 living versed in Moriori customs and traditions, and capable of 

 speaking their language with fluency, also confirmed this infor- 

 mation, and told me that the Kakapo (according to the Morioris) 

 was very abundant in the islands prior to 1836. He himself in 

 the early days had seen their burrows often. I had observed, 

 while collecting, several Psittacine bones, and on learning this 

 fact I felt sure that those I had picked up and packed away must 

 belong to Stringops. On my arrival here, however, I find so far 

 that there are no Kakapo bones in the collection, the Psittacine 

 bones being the head and beaks of Nestor notabilis, the Kea. 

 I have as yet had time to do no more than run through the 

 collection I have brought back ; but there appear to be in it 

 several large Ralline tibiae of species unknown to me. I am 

 looking forward to another opportunity of thoroughly exploring 

 these interesting islands with more time at my disposal than I 

 could afford on this occasion. Henry O. Forbes. 



Canterbury Museum, February 23. 



Pigments of Lepidoptera. 



A LETTER of mine on the subject of butterfly pigments was pub- 

 lished so recently in Nature (December 31, i89i,p. 197) that I 

 hesitate to ask for further space at the present time. But the 

 appearance of Mr. Perry Coste's articles, together with the tone 

 of some remarks made by him at the close of the last article, 

 lead me to venture upon a few words, partly in criticism of a 

 theory he advances, and partly (though this is less important) in 

 claim of priority, since Mr. Coste does not do me the honour 

 to refer to my work on the subject. 



The chief generalization which Mr. Coste bases upon his 

 experiments is that which he terms the "reversion effect,"— that 

 is to say, the production of yellows from reds by the action of 

 acids, and the restoration of the former by neutralization and 

 other means. The theory that he advances to explain these 

 phenomena— namely, that the red body acts as a base, and forms 

 with acids salts which are yellow— is quite untenable. As I have 

 shown (Proceedings of the Chemical Society, June 1889 ; vide 

 Nature, vol. xl. p. 335), the soluble yellows are themselves 

 acid bodies of quite definite composition. Indeed, as far back as 

 187X, Prof. Meldola called attention to the fact that the pigment 

 of G. rhamni was soluble in water, and showed that its aqueous 

 solution had an acid reaction. Mr. Coste has worked with D. 

 eucharis ; if he will dissolve the red pigment from the border 

 of the hind wing of this insect in pure wa'er, he will find that 

 a yellow solution is the result, but that, if the solution be 

 evaporated to dryness, the solid residue of pigment is red once 

 more ; showing that there is eith'er the question of hydration to 

 consider, or a weak combination of the yellow acid body with a 

 base, which is dissociated in aqueous solution. At any rate, I 

 have obtained from this red pigment of eucharis a silver com- 

 pound which contains a percentage of metal exactly equal to 

 that from the pi^^ment of G. rhamni. 



In 1889 I was able to predict possible constitutional formulae 

 for the acid yellow pigments, and am happy to say that recent 

 careful combustions of their silver salts to a large extent confirm 

 my original ideas. My results will be shortly published in 

 extenso. 



Mr. Perry Coste's experiments are very useful as forming a 

 method of classifying these lepidopterous pigments ; but, if he 

 will forgive me for saying so, they are of far too empirical a 

 nature tor any considerations as to the constitution of the bodies 

 to be based upon them. As one who has for many years past 

 spent a large portion of his tiuie and no inconsiderable portion ' 

 of his substance in obtaining a sufficiency of these pigments for 

 analysis and investigation, Mr. Coste will forgive me if I do not 

 respond to his invitation to leave him "to continue his 

 researches alone." It is hardly well for one investigator to say 

 "hands off"" to another, and I shall not imitate Mr. Coste in 

 this matter ; but will only express a hope that in his future work 

 he will not confine himself to the immersion of the wings of his 

 insects in strong and destructive reagents. 



I have lately been working at the genesis of these pigments in 

 the pupae, and might say something with regard to the nature of 



NO. II 73, VOL. 45J 



the group which Mr. Coste labels as doubtfully pigmentary ; but 

 for the present I have sufficiently trespassed upon your space. 

 F. GowLAND Hopkins, 

 Guy's Hospital, S.E., April 9. Gull Research Student. 



"C.G.S. System of Units,' 

 The new edition of Prof. Everett's "C:G.S. System of 

 Units" contains, at the very beginning, two misleading state- 

 ments, based seemingly on a misapprehension of facts. In so 

 valuable a work, such errors are to be deplored. 



Pp. xiii. and xiv. give an account of weighings made at the 

 International Bureau of Weights and Measures between certain 

 " standard pounds " and the international standard of mass. 



From the statement as given, it would be inferred that there 

 is room for doubt as to the relation between the British standard 

 of mass and the international kilogramme. 



The real facts are, that the standard pounds were only 

 nominally "pounds" ; they were standards with known correc- 

 tions, which, however, have not been applied to the equivalents 

 given on p. xiv. 



The true relation of the Imperial pound to the international 

 kilogramme is given in the Board of Trade Report of Proceed- 

 ings under the Weights and Measures Act, 1884 (p. 4), according 

 to which the Imperial pound = 453*5924277 grammes. 



On p. 34 of "C.G.S. System of Units," Mr, Chaney's results 

 of the weight of a cubic inch of water are discussed, and the 

 conclusion is reached that Mr. Chaney's result differs by o 00 125 

 from the theoretical relation between volume and mass of water 

 in the metric system. 



This result is obtained by comparing Mr. Chaney's results, 

 without reduction to vacuo, with the mass of a cubic centimetre 

 of water. 



Mr. Chaney states that the standard air to which his result is 

 reduced weighs 0'3077 grains per cubic inch. Therefore his 

 result reduced to vacuo is : one cubic inch of water at 62° F. 

 weighs 252-286 + 0*308 = 252-594 grains. 



If we take the value for the thermal expansion of water, in 

 terms of the hydrogen thermometer scale, as determined at the 

 International Bureau, we find the density of water at 16° -667 C, 

 = 62° F., referred to its maximum density = 0-998861. 



Using the equivalents I metre — 39 '3 700 inches, and i 

 gramme = 15-43235639 grains, we obtain : one cubic inch of 

 water at 62° F. weighs in vacuo 252-6045 grains ; while Mr. 

 Chaney found 252-594 as above given, a discrepancy of one 

 part in 25,000 only, as compared with one part in 800, given by 

 Prof. Everett. It is not clear from Mr. Chaney's statement 

 whether his weight in air is against brass or other weights ; 

 therefore the vacuum reduction above applied is uncertain by a 

 small amount. O. H. Tittmann. 



Washington, D.C., March 10. 



Mr. Tittmann thinks the true relation is, without doubt— 

 I pound = 453*5924277 grammes. 

 Prof. W. H. Miller determined it to be — 



I pound = 453*59265 grammes, 

 which is the value given on the Card of Equivalents published 

 by the Board of Trade. If the determination quoted by Mr, 

 Tittmann from a Board of Trade Report of 1884 was made 

 under such conditions as to render it authoritative, it is a pity it 

 has been allowed to remain for eight years buried in a Blue- 

 book. One would have expected some intimation of it to be 

 given to scientific men through the Royal Society or in the pages 

 of Nature. 



As regards the three "standard pounds" which were com- 

 pared with standards at the Bureau International in 1883, Mr. 

 Tittmann says they had known corrections. This is not stated 

 in the Travaux et Memoires, where the account of the com- 

 parison is given. There is, however, in the case of the two 

 which are of gilded bronze, a reference to a description of them 

 by Prof. Miller in his paper on the standard pound (Phil. Trans, 

 1856), and, on turning to it, I find that their errors, as stated by 

 him, do not agree even approximately with the determinations 

 made at the Bureau. They differ even in the first significant 

 figure of the error, which is the sixth figure of the entire value ; 

 .«o that, as far as this evidence goes, the five figures 45359 are 

 all that are certain. 



