June 1 8, 1874] 



NA TURE 



137 



considerably widened, and an absorption-band is seen in the 

 green, apparently coinciding with the double sodium line, which 

 comes next in strength to the D lines. All the colours, therefore, 

 seem to be shut out except part of the orange, part of the green, 

 and the ultra blue. As the sodium vapour becomes less dense 

 more light ]>asses through, and the same absorption-bands are 

 seen as are observed in the other method. The vapour then has 

 a slight bluish-green tint, but is nearly colourless. 



The following numbers give the wave-lengths of the more re- 

 frangible edge of the sodium absorption-bauds in tenth-metres 

 obtained in the manner above described : — 



6668 \ 

 6616 



6552 I 

 O490 [ " 

 6450 

 6405 



The drawings accompanying the paper show the general ap- 

 pearance of the two absorption-spectra. 



Linnean Society. — Anniversary Meeting, May 25. — G. 

 Busk, vice-president, in the chair. — The chairman announced 

 the officers who had been elected for the year (see Nature, 

 vol. X. p. 72). — It was moved by Mr. Busk, seconded by Mr. 

 Carrathers, and carried unanimously : — "That the secretaries be 

 requested to convey to Mr. Bentham the cordial thanks of the 

 Society for his invaluable services throughout the thirteen years 

 during which he has occupied the president's chair, to express to 

 him the regret with which the P'ellows contemplate the loss of 

 his serx'ices, and to assure him that the zealous interest which he 

 has taken in the welfare of the Society and the great efforts 

 which he has made with so much liberality and success, to in- 

 crease its prosperity and usefulness will always be held in grate- 

 ful remembrance. " — It was moved by Mr. Busk and unanimously 

 resolved : — " That the thanks of the Society be also given to 

 Mr. Stainton on his retirement from the office of secretary, with 

 an expression of the Society's deep regret on losing his valuable 

 services in that capacity." 



June 4. — Mr. G. J. Allmann, president, in the chair. — The 

 president exhibited a number of living specimens of fire-fly 

 (Luiioln ilalicn) recently taken by himself in the neigh- 

 bourhood of Turin, calling attention to the remarkable syn- 

 chronous emissions of flashes of light by numerous individuals, 

 and pointing out that the phosphorescence is a phenomenon not 

 of darkness merely, but of twilight or night. — Prof. TUiselton 

 Dyer described the structure of the flowers of Fritr^ha and 

 Lyallia, which had recently been sent to this country for the first 

 time by Mr. Moseley, from Kerguelen's Land, and which had 

 been analysed by Prof. Oliver, and subsequently by himself. 

 Dr. Hooker pointed out that several peculiarities in the stiucture of 

 Pringlea, the absence of petals and of the usual glands between 

 the bases of the stamens, the exserted anthers, and the papilla; of 

 the stigma extended into a tuft of hair, appeared to point to this 

 plant (a native of a country where there are no winged insects), 

 being a wing-fertilised member of a class of plants that are ordi- 

 narily fertilised by insects. — The loUowing papers were then 

 read : — I. Contributions to the botany of the C/ialleii'cr expedi- 

 tion. Presented by Dr. J- D. Hooker, C.B.— Xllir. ChalUtiger 

 Lichens (Cape de Verdes), by Dr. J. Stirton. — XVIL;. T^etter 

 from Mr. PL N. Moseley to Dr. Hooker, dated Cape Otway, 

 Australia, March 16, On the botany of Kerguelen's Land, Marion, 

 and Heard Islands. — XVIII. List of hitherto unrecorded species 

 from Kerguelen's Land, Marion, and Heard Islands, with a note 

 on Lyallia kerguchnsts Hook f., by Prof. Oliver. — .Synopsis of 

 the mosses of the Island of St. Paul, by W. Mitten (Appendix 

 to Dr. Hooker's paper On St. Paul's Island plants). — On the 

 Restiacecc of Thunberg's herbarium, by M. T. Masters, F. R. S. 

 At the time that the author^ published his monograph On 

 the South- African Restiacea", in the Journal of the Society, vol. 

 viii. p. 211, and vol. x. p. 209, he had had no opportunity of 

 examining the type specimens described by Thunberg. The few 

 figures published by that naturalist are excellent ; but his descrip- 

 tions are often so imperfect that not even the sex of the plant is 

 mentioned. In common therefore with all who had previously 

 studied these plants, the author hnd to guess at the species in- 

 tended by Thunberg. Lately, however, by the kindness of the 

 authorities at Upsal, Thunberg's African collections have been 

 transmitted to Kew for examination, and the author availed him- 

 self of the opportunity to study the Restiaceas. The paper now 



read contains a list of these specimens with their names, synonyms, 

 and such rectifications in the nomenclature as the examination 

 rendered necessary. —On Napoleona, Omphalocarpnm and 

 Asteranthos, by J. Miers. The plants forming the small group of 

 the Najtoltvneic are confined to two very heterogeneous genera, 

 one from Africa, the other from Brazil. Napolcoim was dis- 

 covered in 1787 at Owaree, by Palisot-Beauvois ; Asteranthos 

 was established in 1S20 by Deslontaines, when he associated it 

 with Napoleona as a group belonging to Symplociiuw. These 

 plants have been ever since a complete puzzle to botanists, 

 who have assigned to them remotely dissimilar positions, 

 the last being that given by the authors of the "Genera 

 Plantarum," who make them a sub-tribe of Lecythidea;, one 

 of their tribes of Myrtacea;. A careful examination of 

 these plants has convinced the author that most botanists have 

 been wide of the mark in regard to their true affinity. Mr. 

 Miers brought forward a large mass of information concerning 

 Napokona, from which he drew the conclusion that there is 

 nothing in its structure to show the slightest relation to Myrtacea; ; 

 that it is equally irreconcilable with the Barringtonieie and with 

 Lecythidea; ; and in consequence of these negative results we 

 must search elsewhere for its true affinity. This'led the author to 

 examine Omphalocarpum, a genus from the same region as Napo- 

 lcoim, and whose flowers and fruit of similar form grow upon the 

 trunk of the trees. This genus has been generally I'egarded as 

 belonging to Sapotacea; ; but the authors of the " Genera Plan- 

 tarum " place it in Ternstrcemiacea:. Ahipoleona cannot, it 

 is true, belong to Sapotacea: ; but as it offers so many points 

 of resemblance, and as it cannot find a place in any known 

 natural order it must remain the monotype of a distinct family, 

 to be placed in juxtaposition with Sapotacea;. In regard to 

 Asteranthos the author shows by analytical figures that it bears 

 scarcely any resemblance in any of its features to Napoleona. 

 A strong resemblance exists in the form of its calyx to that repre- 

 sented by Wight in an Indian species of Rhododendron. And 

 there seems nothing therefore to separate Asteranthos from other 

 genera of Rhododendrere, except its more rotate corolla. 



Mathematical Society, Thursday, June 11. — Dr. Hirst, 

 F.R.S., president, in the chair. — The president made a state- 

 ment to the effect that he had much pleasure in announcing to 

 the members present that he had received a letter from Lord 

 Rayleigh in which that gentleman expressed his intention of 

 handing over to the Society the sum of 1,000/. to be invested 

 and applied to assist in the publication of the Proceedings, and 

 the purchase of mathematical periodicals. As the subject will 

 be brought before the members more fully in November next, 

 no further action was taken, but the announcement of the muni- 

 ficent offer gave general satisfaction to the meeting. — Prof. 

 Cayley, F.R. S., V.P., having taken the chair, Mr. S. Roberts 

 gave an account of his paper On the parallels of developables 

 and of curves of double curvature. — Lord Rayleigh next read a 

 note On the numerical calculation of the roots of fluctuating 

 functions. — In the absence of the authors, the secretary read 

 parts of papers by Mr. Griffiths and Mr. Routh, F. R. S. In his 

 note On a remarkable relation between the difference of two 

 Fagnanian arcs of an ellipse of eccentricity c, and that of two 



corresponding arcs of a hyperbola of eccentricity— Mr. Griffiths 



e 



.11-1 »i, r II ■ II- ^rc /IP, —arc QQo 



establislies the iollowmg relation: =~ ^.-.ivri" 



=" arc P^P^- arc Q}- Q^ 



where the unaccented letters refer to the ellipse and the accented 

 letters to the hyperbola, and x, |, .\o, fo are the abscissa: of 

 P, ft Po< Qo- 'fhe object of Mr. Routh's first paper, viz. Sta- 

 bility of a dynamical system with two independent motions, will 

 be gathered from the following extract: — "The equations of 

 motion of a dynamical system performing small oscillations with 

 two independent motions are of the form 



^,1^ ^dx ^ ^^_ ^p<Pl^ Qdy fj 



dt- dt dt- dt ■' 



A^ ^ -f ^i-^- -^ Ox + F^ ^'1 -H Glf + Ily^ = o 

 dt^ dt dl^ dt -^ 



To solve these we eliminate either x or y, and obtain a bi- 

 quadratic of the form 



aDi + dD^ + cD' + dD + c =^ o 

 The whole nature of the motion depends on the forms of the 

 roots of this (quation. Rules are given in books on the theory 

 of equations lo determine whether the roots are real or imagi- 

 naiy, but this is not exactly what we want to know. It is often 



^ollo 



