October 25, 1894] 



NATURE 



62 



and its properties since 1875, when the first edition was pub- 

 lished, have been taken into account. The work now consists 

 of four parts. The first part deals with timber in general ; in 

 part ii. the timbers of Dicotyledonous trees are considered ; 

 part iii. deals with Coniferous timber trees ; and the fourth 

 part chiefly consists of tables showing the results of experi- 

 mental investigations on the physical properties of timber. 

 The book has been of valuable service to the shipwright and 

 carpenter from the time it first appeared ; and Prof. Ward's 

 revision has certainly given it a new lease of life. 



The appearance of a second edition of Lord Rayleigh's 

 " Theory of Sound " (Macmillan and Co.) reminds us that the 

 first edition was reviewed in these columns by that eminent 

 investigator, Hermann von Helmholtz, nearly seventeen years 

 ago. Much additional matter has been included in the new 

 edition, and the subject is carried to the limits of the present 

 state of knowledge. Two new chapters have been interpolated, 

 devoted to curved plates or shells, and to electrical vibrations. 

 It was the author's original endeavour to produce " a connected 

 exposition of the theory of sound, which should include the 

 most important of the advances made in modern times by 

 mathematicians and physicists." This object has bee", borne 

 in mind in the preparation of the new edition. Lord Rayleigh 

 naturally inclines to physical methods of investigation, but 

 purely mathematical solutions are not entirely eschewed. The 

 work has been recognised as a masterly exposition of a difficult 

 subject ever since it first appeared, and the second edition 

 maintains the high standard of the original. 



A.N" important memoir concerning nitrogen Irioxide, nitrous 

 anhydride, NoOj, is communicated by Prof. Lunge and 

 Herr Porschnew to the current issue of the Zcitschrift fiir 

 Anorgaiiische C/iemie. It is claimed that the investigation, whose 

 results are now published, finally disposes of all doubt as to the 

 existence of this much discussed oxide of nitrogen. The main 

 conclusion derived from the work is that nitrogen trioxide is a 

 well characterised individual substance, which is readily formed 

 under ordinary atmospheric pressure below the temperature of 

 - 21° by the union of nitric oxide NO and nitrogen pero.xide 

 N„Oj,and constitutes an indigo-blue liquid. It is stated to be per- 

 fectly stable at and below this temperature ; but at a temperature 

 slightly superior to this, even under pressure, it commences 

 to decompose, and the dissociation is almost complete upon the 

 conversion of the liquid into gas. Nitrous anhydride in a 

 condition of purity thus appears to be incapable of existence 

 in the gaseous state, while forming a comparatively stable 

 liquid at temperatures below -21'. The gaseous product of 

 dissociation, a mixture of nitric oxide and peroxide, exhibits 

 similar chemical properties to those which might have been 

 expected of gaseous nitrogen trioxide, hence of course the 

 diSicuUy which has been experienced in deciding the question. 

 It is pointed out, however, that the absolute incapability of 

 existence of gaseous molecules of nitrogen trioxide is not 

 proved, and the results of the investigation would appear to 

 indicate that a residue of such molecules does escape dissociation 

 upon the passage of the liquid into the gaseous state, and exists 

 side by side with the molecules of the decomposition products. 

 The experiments upon which these conclusions are based are 

 mainly the following. It was first established that nitric oxide 

 and nitrogen peroxide exhibit only the very slightest 

 inclination to unite chemically at the ordinary tem- 

 perature and at temperatures up to 100°. It was next 

 found that at the temperature of - 21° the two oxides 

 combined in practically exactly molecular proportions to form 

 the indigo-blue liquid. The exact amount of N0O3 present in one 

 of the specimens analysed is stated to have been 98 '3 per cent. 

 The well known work of Ramsay and Cundall upon this subject 



NO. 1304, VOL. 50] 



is, of course, quoted, and it is stated that the apparently small 

 amount of absorption of nitric oxide by liquid nitrogen 

 peroxide, conespondingto only 3-5 percent, of N.O„ observed 

 during that investigation, was due to the loss of weight by 

 mechanical removal of a portion of the nitrogen peroxide in the 

 stream of issuing nitric oxide. It was further demonslrr.ted 

 that the product of the action of oxygen upon nitric oxide gas 

 behaves, particularly towards sulphuric acid, precisely like a 

 mixture, which it probably is, of nitric oxide and nitrogen 

 peroxide. Moreover, the vapour derived from liquid nilrogen 

 trioxide is not stable towards oxygen, but becomes further 

 oxidised until it is almost pure peroxide. The memoir will be found 

 to include an admirable summary of the literature of the subject, 

 together with the views of Prof. Lunge concerning the bearing 

 of the main conclusions of the investigation upon the theory ol 

 the sulphuric acid manufacture. 



The additions to the Zoological Society's Gardens daring the 

 past week include a Vervet Monkey (Cercopilhectis lalandii) 

 from South Africa, presented by Mr. Seymour Willoughby ; 

 a Pig-tailed Monkey (Macaeus nemeslrittus) from Java, pre- 

 sented by Mr. H. M. Vincent : a Tiger {Felis tigi-is) from Amoy, 

 China, presented by Mr. Robert Bruce ; a Tiger Cub (Felis 

 tigris) from Burmah, presented by Mr. John Halliday ; a Ring- 

 tailed Coati (Nasua rufa) from South America, presented by Mr. 

 J. E. Symonds ; twoBrazillianCaracaras (/'()/)'^i>rK/(Sraj(7»>K«'r) 

 from South America, presented by Lord Lilford ; two Grey- 

 breasted Parrakeets (Bolborhyitchiis monaehu!) from Monte 

 Video, presented by the I nns of Court Hotel Company ; an 

 Egyptian Jerboa (Difus agyptius) from Egypt, a Patagonian 

 Conure (Contirus falagontis) from La Plata, two Brazilian 

 Cariamas (CaWawa .;«V/a/a) from South-east Brazil, deposited. 



OUR ASTRONOMICAL COLUMN. 



Triangulation of Sixteen Stars in the Pleiades. — 

 In addition to the great interest that has always been attached 

 to this bright group of stars, the Pleiades, as can be gathered 

 from the numerous myths (Nature, vol. xlix. p. 366) which have 

 been handed down to us, their value to the practical astronomer 

 has been by no means small. In most astronomical measure- 

 ments, observations have first to be made on stars the positions 

 of which are accurately known, in order to determine the in- 

 strumental constants : thus, for instance, the pitch of micro- 

 meter screws, ring micrometer constants, &c. The Pleiades, 

 as they consisted of a group of bright stars suitable for such 

 determinations, were constantly used for these purposes, and 

 this necessitated a previous complete knowledge of their posi- 

 tions and motions. 



At the present day, however, the stars in the Pleiades group 

 are rather of too bright a nature and too varied in magnitude 

 for very accurate determinations of instrumental constants, and 

 the tendency is now to turn to that group of stars in Perseus, 

 which is more suitable in many respects. A recent triangulation 

 of this region has lately been undertaken by Prof Wilhelm 

 Schur at Gottingen, with the large heliometer, the results of 

 which appeared in the ProceeJin!;^ of tht Royal Sodety oj 

 Sciences of Gctlingen. The triangulation to which we wish to 

 refer is of sixteen stars in the Pleiades, and has been made by 

 Dr. Leopold Ambronn at the Gottingen Observatory {Astro- 

 notnische Mitthcilungen von der Koniglichen Sternc-varte zu 

 Gottingen, Bd. xxxix. 3 part). 



The instrument employed, a good illustration of which is 

 given, was the small Eraunhofer heliometer, which in earlier 

 times was used in the two Venus Expeditions of this century. 

 It might at first sight seem superfluous to attempt this triangula- 

 tion with such a small instrument, when we are already ac- 

 quainted with the results obtained from larger heliometers. 



The value of this investigation lies, however, in the very 

 minute determinations of the instrumental constants, and these 

 would be interesting even if nothing more were attempted. 



Dr. Ambronn has, however, after making these instrumental 

 constant determinations, measured the positions of sixteen of 

 the Pleiades stars, and compared them with the results obtained 



