6:,2 



NA TURE 



[October 17, 1907 



are various exceptional cases of anomalous dispersion, and 

 to cover these a modified theory of uniaxal crystals is 

 given in the following terms. The molecules (or crystal 

 units) of the medium are not necessarily to be supposed 

 ellipsoidal in shape, but are optically aeolotropic, so that 

 the subsidiary equations connecting the polarisation of a 

 particle with the effective electric force are leolotropic, 

 with an axis of symmetry ; the particles are supposed to 

 be arranged in a homogeneous assemblage, such that the 

 effective cavity may be taken as a spheroid of small 

 ellipticity with its axis of symmetry coincident in direction 

 with that of the crystal unit. Hence an explanation is 

 given of the anomalous dispersion of the double refraction 

 in regions free from absorption, that is, when a medium 

 composed of the same crystal units arranged in regular 

 cubical order would give regular dispersion. The theory 

 is considered finally in its general application to dis- 

 persion in biaxal crystals. 



The author has attempted to connect the varieties of 

 dispersion of double refraction with the structure of the 

 crystal under the following assumptions. The crystal unit 

 contains vibrating electrons, so that their combined effect 

 is expressed by three principal equations connecting the 

 polarisation of the unit with the effective electric field ; if, 

 then, these units are arranged in regular cubical order, we 

 have a medium with principal refractive indices along three 

 fixed directions in space, and in this case it is assumed 

 that there is regular decrease of the double refraction with 

 increasing wave-length in regions away from absorption 

 bands ; but considering in general any other homogeneous 

 assemblage, the effect is expressed by a change in the 

 effective electric field acting on the crystal unit ; this 

 effect is estimated by supposing, as a sufficient approxim- 

 ation, that the effective cavity is slightly ellipsoidal in- 

 stead of being spherical. Thus differences of packing of 

 the crystal molecules .are represented optically by variations 

 in the ratios of the axes of the effective cavity and in 

 their directions in space compared with the polarisation 

 axes of the individual unit. Combining these assumptions, 

 it is shown that they are sufficient for a descriptive theory 

 covering the varieties of dispersion of double refraction 

 found in natural crystals. 



P.ARIS. 



Academy of Sciences, October 7. — M. Henri Becquerel 



in the chair. — The spectrum of the Daniel comet, 1907^ : 

 Jean Bosler. The spectrum of the nucleus of the comet 

 was photographed on the nights of .August 8 to 9, 18 to 19, 

 and 19 to 20, with exposures of forty minutes, one hour, 

 and one hour and ten minutes. Details are given of the lines 

 observed, which appear to indicate the presence of hydro- 

 carbons and cyanogen. There are also some lines of which 

 the origin is uncertain. — Trigonometric series : Marcel 

 Riesz. — The execution of a geodesic chain of precision in 

 the Savoy .Alps : Paul Helbronner. Particulars are given 

 of the immediate objects of the survey, together with a list 

 of the thirty-three stations, mostly mountain peaks, pro- 

 posed to be included in the survey. Of these, twenty-six 

 were completed bevween June 12 and September 28. — 

 Spectroscopes with mirrors ; Maurice Hamy. The substi- 

 tution of mirrors for objectives is often used in spectro- 

 scopes. The present note gives a study of the theory of 

 the best position to give the face of the last prism or 

 grating to obtain a field of images as flat and as extended 

 as possible. — The thermoelectricity of nickel ; the influence 

 of foreign metals : H. Pecheux. Three specimens of 

 nickel were studied, the chemical analysis of each being 

 determined. Couples were formed of each of these with 

 pure copper, and the thermoelectromotive forces studied 

 for a temperature range of 640° C. The curves of electro- 

 motive force of the three couples were .not parallel, but 

 the results are comparable, differing only bv about 025 per 

 cent, on the average. The simultaneous existence of 

 copper and cobalt in a specimen of nickel produces the 

 most marked deviations of E.M.F.— Phenyl migrations in 

 the aronatic iodohydrins by the elimination of HI from 

 the same atom of carbon ': M. . Tiffeneau. The thcorv 

 developed in previous papers regarding the migration of 

 the phenyl group in compounds of the type 



(.Ar)R— C(OH)— CHI— R' 

 NO. I9S1, VOL. 76] 



has been extended and confirmed by a study of the corre- 

 sponding ether oxides. — The phases of development of the 

 Epicaridse ; experimental verification of the nature of the 

 Microniscidse : Maurice Caullery. — The presence of 

 Tyroglyphinae in the long bones of the wings of birds : 

 E. L. Trouessart. — The existence of slatoblasts in the 

 scvphistome : Edgard K^rouard. — The necessity of 

 cultures in the study of the gonococcus : .A. Guepin, The 

 absence of the gonococcus, and of any other pathogenic 

 microbe, can only be admitted as proved after negative 

 results have been obtained from systematic cultures. — Some 

 new fossil plants from the travertine of Suzanne : Ren6 

 Vieruier. 



DIARY OF SOCIETIES. 



PRIDAY, October 18. . 



Institutiok of Mechanical Engineers, at P. — The Indicated Power 

 and Mechanical Efficiency of the Gas Engine : Prof. B. Hopkinscn. 

 THURSDAY, October 24. 



Chemical Society, at 8.30.— The Constifution of Phenol- and Quinol" 

 phthalein Salts : a Contribution to the Quinonoid Theory of Colour • 

 .■\. G G.een and P. E. King.— Poly-ketides : J. N. Collie.— Produclion 

 of Orcinol Compounds by the Aclion of Heat on the Sodium Salt of 

 Elhylaceloacetate : J. N. Collie and E. R. Chrystall.— A Simple G.is 

 Generator for Analyiical Operations: I. M, Sanders.— Some Double 

 Kerrocyanidcs of Calcium, Potassium and Ammonium : J. Campbell 

 Brown. — Halogen Determination in Organic Substances: J. Moir. — 

 Racemisation by Alkali as applied to the Resolution of r-Mandelic .'^qid 

 into its Optical y Active Isomerides: A. McKenzie and H. A. Mtiller.— 

 The optical Activity of Cyclic Ammonium Compounds ; F. Buckney and 

 H. O. Jones.— Kelen. A Ne* Anhydride of .\cet c -Acid: N. T. M. 

 Wilsmore.— The Aciion of Phosphorus Penlachloride on Hydroxy-tri- 

 methyl Succinic Ester, i : 2- Dimethyl Trimelhylene i : 2.DicaTboxyiic 

 Acid : H. Henstock and B. E. Woolley. 



CONTENTS. PAGE 



Stereochemistry. By F. M. P 609 



Oriental Plague. By Prof. R. T. Hewlett 609 



Memoirs on Marine Animals. By J. H. A. . . . 610 



A Life of Sir William Flower. By K. H. T 611 



Our Book Shelf: — 



Andreini: " Sfere cosmografiche e loro applicarione 

 alia lisoluzione di Probleiiii di Geographia 



Matematica " 612 



Biooks and James: "Electric Light and Power." — 



M. S 612 



Ileiicourt: " L'Hygiene moderne." — R. T. H. . . 612 

 Letters to the Editor. — 



The Advancement of Science. —Dr. W. N. Shaw, 



F.R.S 613 



On Correlation and the Methods of Modem Statistics. 



(n/iislraUd.)—'PTo{. Karl Pearson, F.R.S. . . 613 

 The Body of Queen Tii.— Prof. G. Elliot Smith, 



F.R.S 615 



The Interprelatii-n of Mendelian Phenomena. — R. H. 



Lock . . 616 



The Colour of Dye Solutions.— Dr. S. E. Sheppard 616 

 The Convection Explanation of Electrolysis. — J. 



Brown, F.R.S 617 



Classification of Portraits. (Ilhistrated.) By Dr. 



Francis Gallon, F.R.S 617 



Weights and Measures Regulations 618 



Ancient Khotan. (lUustraled.) By H. R. Hall . . . 6:9 



International Meteorological Committee 620 



Notes .... 620 



Our Astronomical Column : — 



A New Comet . 624 



Sun-spot Spectra 624 



The Red Spot on Jupiter 625 



The Proper Motions of Stars in the Cluster Messier 92 625 



The Dominion Observatory, Ottawa 625 



The Perseid Meteors 625 



Botanical Congress at Dresden. By T. J 625 



Water and Ice, To-day and in the Glacial Epoch. 



(/lliislrah'd.) By G A. J. C 626 



Endowments for Secondary Education. By G. F. 



Daniell 617 



University and Educational Intelligence 630 



Societies and Acaaeoiies 631 



Diary of Societies 632 



