July 4, 1878] 



NATURE 



2CI 



upper part for a distance of eighteen yards thrown into the field. 

 Then came about 9 yards of wall quite undisturbed, and after- 

 wards thirty-six yards half down, but lying in the roadway on 

 the opposite side of the wall. About seventeen yards of the 

 coping-stone at the extreme northern end of the broken wall was 

 also thrown into the road. 



Fortunately the whole lay at the time of our visit just as when 

 the whirlwind had passed, and proved conclusively that, in this 

 case at least, the order of rotation was the same as that of the 

 cyclones of the northern hemisphere. Thomas Dobson 



Marine School, South Shields, June 22 



I 



Zoological Geography — Didus and Didunculus 



I AM at a loss to understand how Didunculus can be called 

 "a near congener" of the Dodo, as Mr. Searles V. Wood, 

 apparently following Dr. Litton Forbes (whose paper I have 

 not seen), terms it {suprh, p. 220). The two birds, so far from 

 being congeneric, belong to perfectly distinct groups of the 

 Order Columbce, and nearly thirty years ago Bonaparte treated 

 them as the types of distinct families — Didida and Didunculida 

 — an example which has been generally followed by the best 

 authorities. If Mr. Wood will refer to a paper in the Philo- 

 sophical Transactions for 1869 (pp. 327-362) I think he will see 

 that there is good ground for not attaching much importance to 

 the slight and superficial characters in which Didunculus resembles 

 the Didida. Alfred Newton 



June 30 



A Subject-Index to Scientific Periodical Literature 



I BEG permission to ventilate in your columns a subject which 

 must make itself felt more or less to all your readers, viz., the 

 want of some subject-index to the vast amount of material scat- 

 tered about in the numerous scientific periodical publications of 

 the present day. It is true we have the admirable catalogue of 

 the Royal Society, but unless you are acquainted with the name 

 of every author who has wTitten on your subject, it is nearly 

 hopeless attempting a complete bibliography of it. Now I would 

 suggest whether an index to the Royal Society's catalogue cannot 

 be made on the same plan that has been adopted by the com- 

 mittee of the new edition of " Poole's Index," viz., by getting 

 different societies, libraries, or individuals to take certain parts 

 of the work. ITie following is a short abstract of how this 

 conmiittee have set about their work ; any of your readers who 

 wish for further information will find it at pp. 109-206 of the 

 '* Transactions and Proceedings of the Conference of Librarians, 

 London, 1878," and on p. 201 a short specimen may be seen. 

 The index is made on sheets of foolscap, and the indexer has 

 nothing to do with alphabetical arrangement ; he makes his 

 entnies in the order the articles occur in the volume at which he 

 is working ; these sheets are then sent to the editors, who cut 

 ^them into slips and work them into alphabetical order with 

 the material coming in from other sources. By this method 

 complete uniformity is maintained ; for should the indexer have 

 a peculiar idea of his own how any particular part should be 

 done, his peculiarity is put right at the central bureau or editorial 

 office. 



I have said this should be an index to the Royal Society's 

 catalogue, but if this scheme is ever carried into execution I 

 would strongly urge that the index should be made from the 

 periodicals themselves, and not from the entries in the Royal 

 Society's catalogue, as it is absolutely impossible to index a 

 paper properly from the title only ; and another advantage is 

 that under this plan the work could be better carried out, as 

 each indexer could confine himself to his own branch of study ; 

 whereas if the index were made from the catalogue itself, it 

 must be cut up into alphabetical portions, and each man would 

 have to do a variety of subjects. This may seem to many too 

 large a matter even for consideration, but for many years so was 

 a good alphabetical catalogue of the different scientific papers ; 

 this has been conquered by the Royal Society, and if that learned 

 body would constitute itself the central bureau, I think willing 

 workers would soon be found, and the success of the index be 

 assured. Of course all this would cost money, but surely an 

 appeal might fairly be made to scientific societies and individuals 

 to help in this work, which would be so great a help to the 

 "advancement of science." Jas. B. Baii.ey 



Oxford 



A NEW TRIUMPH OF CHEMICAL SYN- 

 THESIS 



'T^HE year 1868 was a marked epoch in the progress of 

 -*■ chemical synthesis as well as of tinctorial processes. 

 The German chemists, Profs. Graebe and Liebermann, 

 succeeded at that date in preparing from the hydrocarbon 

 anthracene manufactured from coal tar the brilliant dye- 

 stuffs hitherto won from madder, and in establishing 

 also the chemical constitution of these various com- 

 pounds and their relationship to other well-known bodies. 

 This was the first instance in which the chemist had 

 succeeded in artificially preparing colours occurring in 

 the vegetable kingdom ; and although the manufacture of 

 artificial madder colouring matters has assumed at the 

 present day colossal proportions and bids fair to entirely 

 supersede the preparation of the natural products, it 

 has hitherto remained the only instance of the kind in 

 the history of chemistry, all other vegetable and ani- 

 mal dyes obstinately refusing to disclose the secret of 

 their composition and be classified among the compounds 

 of well-defined molecular structure. Within the past few 

 weeks the madder colours have ceased to occupy this 

 unique position. Modern chemistry has succeeded in 

 preparing synthetically none other than common indigo, 

 the well-known product of the halts tinctoria, and Nerium 

 tinctorium of India and South America. 



This discovery is likewise due to a German chemist, 

 Prof. A. Baeyer, the genial successor to the chair of 

 Liebig at Munich, one of the most indefatigable and suc- 

 cessful investigators of our day. For a score of years he 

 has been seeking to solve the problem of the constitution 

 of indigo and its synthetical preparation. Slowly and 

 patiently he has gathered together and elaborated one 

 fact after another, until finally, at the last session of the 

 German Chemical Society, he was able to announce the 

 completion of the long research and the discovery of the 

 last link in the chain of synthetic reactions leading to the 

 formation of indigo. 



We will sketch briefly the various steps in this syn- 

 thesis, which is not only one of the most brilliant chemical 

 achievements of the present year, but affords an unusually 

 interesting glimpse into the methods and aims of the 

 modem chemist. 



Indigo blue, or indigotine, possesses the formula 

 QHgN O, and, from the products of its decomposition, 

 aniline, orthoamidobenzoic acid, &c., has long been 

 regarded as closely allied to the benzene series. At- 

 tempts without number have been made to show the 

 nature of this connection by starting from benzene 

 compounds, but hitherto with fruitless results. As in the 

 case of the alizarine compounds, where Graebe and 

 Liebermann first found that anthracene was obtained 

 from alizarine by reducing agents, so has the first step 

 in the solution of the indigo problem been to study care- 

 fully the various compounds resulting from successive 

 decompositions, each in turn yielding a body of a simpler 

 constitution. Passing from one compound to another, 

 Prof. Baeyer finally reached alpha-toluic acid or phenyl- 

 acetic acid, CeH5.CH2.COOH, a not uncommon body, 

 easily prepared from cyanide of benzyl. Here he stopped, 

 and began to retrace his footsteps. 



The first reaction was to replace one of the hydrogen 

 atoms in the phenylic group oi phenylacctic acid, 



(A.) CeHg.CHs.COOH, 



by the group NOg — a familiar operation effected by 

 treatment with nitric acid— and giving, among other 

 compounds, ortJio-nilrophenylacetic acid, 



iv.\ cw XCH2.COOH 



This, when reduced by nascent hydrogen—/.^., sub- 

 mitted to treatment with a mixture of tin and hydrochloric 



