274 



NATURE 



[May 25, 1916 



fiiuch more active nitrogen is obtained from the posi- 

 tive column in a narrow tube than in a wide one. 

 (3) Tlie yield of active nitrogen comes to a limit as 

 the length of positive column traversed by the gas is 

 increased. (4) A trace of oxygen (or almost any other 

 admixture) is known greatly to increase the yield of 

 active nitrogen. The amount of oxygen required to 

 do this considerably increases the fall of potential at 

 the kathode, but it does not measurably affect the fall 

 of potential in the positive column. (5) Active nitrogen 

 is produced by the spark at atmospheric pressure. 

 (6) The metal scattered from a copper kathode when 

 the discharge passes can be made to emit its line 

 spectrum in a stream of active nitrogen. — Dr. R. A. 

 Houstoun : A theory of colour vision. The paper ex- 

 plains the facts of colour-mixing by assuming the 

 existence of one class of oscillators in the retina with 

 a free period in the middle of the spectrum. Owing 

 to disturbing influences, the vibrations of these oscil- 

 lators are never monochromatic, but, when represented 

 by a Fourier integral, contain a range of wave- 

 lengths. Thus, even if the incident light is pure red 

 or pure green, the vibrations contain yellow as well. 

 Hence, if the vibrations of the oscillators are identified 

 with subjective light, simultaneous excitation of the ' 

 eye with red and green produces yellow. — Col. R. L. 

 Hippisley : Linkages illustrating the cubic transforma- 

 tion of elliptic functions. The linkage consists of three 

 parts. First, a closed linkage consisting of three 

 identical three-bar linkages in various phases of de- 

 formation connected together by bars equal in length 

 to the traversing links, which, as has been described 

 in the Proc. Lond. Math. Society, series 2, vol. xi., 

 indicates the positions of the points where the poristic 

 triangle touches its inscribed" circle. Secondly, three 

 positive Peaucellier cells which point out the positions 

 of the vertices of the triangle. Thirdly, a closed 

 linkage similar to the first, which gives the position 

 oi the orthocentre. This orthocentre describes a 

 circle, and it can be shown by a few lines of vector 

 geometry that its angular displacement is the sum 

 of the angular displacements of the circumradii of 

 the _ vertices of the triangle. The angles which these 

 radii make WMth the axis are the double amplitudes 

 of the elliptic functions which express the positions of 

 the vertices, namely, am(M + |5'K)(5' = o, i, 2). 



Llnnean Society, May 4.— Prof. E. B. Poulton, presi- 

 dent, m the chair.— E. A. Bunyard : The origin of the 

 garden red currant. The red currant has been culti- 

 vated from the early fifteenth century, and was at 

 first pure R. viilgare ; for 100 years no variations were 

 recorded. R. petraeum was introduced into gardens in 

 1561 by Konrad Gesner, and a few vears after Came- 

 rarius mentions the "old" red and a new variety, 

 "baccis rubris majoribus." R. rubrum seems to have 

 come into currant history at a later date. The author 

 considers that interhybridisation of the three species— 

 R. vulgare, R. ruhrum, and R. petraeum— is sufficient 

 to account for the numerous varieties of the red currant 

 as grown in gardens to-day, and the supposed effects 

 of cultivation need not in this case be invoked.— Dr. 

 J. C. Willis : The dispersal of organisms, as illustrated 

 by the floras of Ceylon and New Zealand. In two 

 recent papers on the flora of Ceylon, and in a forth- 

 coming one on the flora of New' Zealand, the author 

 had brought forward conclusions on geographical dis- 

 tribution which, if accepted, will remove that subject 

 from the immediate realm of evolution, and show that 

 it may be largely studied by arithmetical methods. 

 Once a species is evolved, its distribution depends 

 upon causes which act mechanically. As all families 

 and genera behave alike, it seems to him that one 

 cause only must be responsible for their behaviour, 



NO. 2430, VOL. 97] 



but a combination of causes may be acting, though in 

 that case each cause must act mechanically on all 

 alike. The cause which seems the determining factor 

 in dispersal is age within the country concerned. — 

 R. J. Tillyard : A study of the rectal breathing appa- 

 ratus in the larvae of the Anisopterid dragon flies. — 

 W. E. Collinge : Description of a new species of Idotea 

 (Isopoda) from the Sea of Marmora. 



Zoological Society, May 9. — Dr. S. F. Harmer, vice- 

 president, in the chair. — Miss Dorothea M. A. Bate : 

 A collection of vertebrate remains from the Har Dalam 

 Cavern, Malta. Birds are most numerously repre- 

 sented, and include some bones of an Anserine bird 

 showing a reduction in its powers of flight. It is 

 believed to be a hitherto undescribed species, and is 

 referred to the genus Cygnus. A list is given of all 

 the species of vertebrates recorded from the Pleistocene 

 cave and fissure deposits of the island. — Dr. J. C. 

 Mottram : An experimental determination of the factors 

 which cause patterns to appear conspicuous in Nature. 

 A series of experiments was carried out with artificial 

 patterns arid backgrounds under controlled conditions 

 of lighting, and 'a large number of determining factors 

 were discovered, both as regards plain and patterned 

 objects and backgrounds. Finally, the experiments 

 showed that the most conspicuous shape and pattern 

 which an object can have, when viewed against a 

 series of plain and patterned backgrounds, was pre- 

 sented by a circular disc of black, with a central 

 circular area of white. Having arrived at this conclu- 

 sion, the Indian diurnal Lepidoptera were completely 

 examined, in order to discover whether any species 

 presented patterns approaching this ideal conspicuous 

 pattern. It was found that a considerable number 

 presented patterns scarcely removed from this ideal, 

 and that a large proportion of these insects are con- 

 sidered to be "protected" species presenting "warn- 

 ing coloration." 



Geological Society, May 10. — Dr. Alfred Harker, 

 president, in the chair. — F. R. C. Reed : Carboniferous 

 fossils from Siam. The fossils described in this paper 

 were collected by the Skeat Expedition from Cam- 

 bridge in the year 1899, at a locality called Kuan Lin 

 Soh, in the Patalung district of Lower Siam, and 

 were briefly mentioned in the "reports" of the British 

 Association for 1900 and 1901. They occur in a pale, 

 fine-grained, jointed siliceous rock, with an irregular 

 or subconchoidal fracture. The field-relations of the 

 beds have not been recorded. The general facies of 

 the small fauna which the available material has 

 yielded indicates a Lower Carboniferous age for the 

 beds, and the affinities of the species seem to be 

 European, and suggest the Culm Series. — H. G. 

 Smith : The Lurgecombe Mill lamprophyre and its in- 

 clusions. A lamprophyre-dyke intrusive into Culm 

 Shales has recently been exposed at Lurgecombe Mill, 

 near Ashburton (South Devon). The rock is compact 

 and fine-grained, small crystals of biotite imparting 

 to it a characteristic lamprophyric appearance ; vesicles 

 with secondary ininerals appear towards the margins. 

 In thin section, idiomorphic biotite, olivine-pseudo- 

 morphs, and felspars are seen to make up the bulk 

 of tiie rock ; chlorite and secondary quartz occupy the 

 interstices. One o'f the thin sections was seen to con- 

 tain crystals of blue corundum associated with mag- 

 netite, in a patch which was obviously foreign to the 

 rock. With the object of obtaining additional 

 examples many slices were cut, sections being made 

 of those that seemed promising. In this way several 

 of these inclusions were obtained, the largest being 

 about 03 in. In diameter. All contain corundum and 

 magnetite, but in some cases staurolite also is present 

 and, more rarely, green spinel. 



