December 8, 1910] 



NATURE 



193 



physical conditions. The paper is based upon a generalised 

 dispersion formula 



a + i/(/»2 - I ) P X- - A -, 



where P is the densitj- of the medium. The quantities 

 i, and X, refer to natural vibrations inherent in the mole- 

 cule, and it is assumed that these are not changed by 

 varying physical conditions, such as temperature, pressure, 

 or density ; thus an attempt is made to express these con- 

 ditions in their optical effect by two variables, P and a. 

 The scheme is tested first by a relation deduced from the 

 above formula, namely, the difference in value of 

 P/(n'— 1) for any two physical conditions of the same 

 substance is constant in regard to wave-length. From an 

 examination of available data this appears to be satisfied 

 approximately for gases and liquids and for changes from 

 gas to liquid. Numerical values of a for various sub- 

 stances in different conditions are obtained by assigning 

 it zero value for the gaseous condition at normal pressure 

 and temperature. Artificial double refraction is included 

 in the same formal scheme by allowing anisotropic changes 

 of the quantity .'. Finally, for dispersion formulae of the 

 above tj'pe an observed maximum of absorption (or of 

 selective reflection) is identified, not with A,, but with a 

 wave-length X',, differing from A, by a term involving P 

 and ir; numerical examples are given for rock-salt and 

 fluorite. The wave-lengths A', are calculated under various 

 conditions for certain substances : experimental data are 

 analysed to show the pressure-displacement for air and 

 the temperature-displacement of absorption maxima for 

 water and carbon disulphide. — C. P. Butler : The spec- 

 trum of Halley's comet. Provision was made for photo- 

 graphing the comet and its spectrum from the beginning 

 of May at Fosterdown, Caterham. Exceptionally bad 

 weather prevented observations until the end of the month, 

 when photographs and visual observations of the spectrum 

 were obtained on May 23 and 26. The photographs of 

 the comet taken with a Dallmeyer lens, 6 inches aperture, 

 50 inches focus, show that the nucleus was at times 

 multiple. Visual observations of the nucleus showed strong 

 continuous spectrum with three bands in the yellow-green, 

 green, and greenish-blue, having approximate wave-lengths 

 5635 (int. 7), 5165 (int. 10). 4737 (int. 7). The spectrum 

 of the coma surrounding the nucleus consisted of these 

 same three bands, without any indication of continuous 

 radiation. The photographic spectra show only the 

 brightest spectra features of the spectrum of the nucleus, 

 the relative intensities differing widely from the visual 

 intensities owing to the selective sensitiveness of the plates. 

 The two most conspicuous bands are near A 4737 (int. 10) 

 and 3884 (int. 6), with fainter bands near AA 4050, 4360, 

 5165, and 5635. Photographs obtained elsewhere at 

 different times show differences in the relative intensities 

 of the component bands. This has been ascribed to varia- 

 tions of atmospheric absorption. It may be noted, how- 

 ever, that before and after the transit of May 19 the 

 aspect of the head would vari- quicklv ; at one time the 

 hotter side facing the sun would be best seen, at others 

 the cooler portions away from the sun would be more 

 prominent. Preliminarv experiments show that by van.'ing 

 conditions of vaporisation the relative intensities of the 

 carbon or hvdrogen bands may be considerably modified, 

 and it would appear that the changes observed in the 

 cometary spectrum might be produced bv some such differ- 

 ence of condition. — Dr. H. F. Baker : A geometrical proof 

 of the theorem of a double six of straight lines. 



Edinburgh. 

 Roval Society, November 7. — Pmf. Cram Brown, vice- 

 president, in the chair. — J. D. Hamilton Dickson : .A 

 thermoelectric diagram from —200° to +100° C, based 

 on the experiments of Sir James Dewar and Prof. 

 Fleming. The platinum temperatures were first reduced 

 to absolute scale. The observations of the electromotive 

 fbrce of each metal-lead couple were plotted against 

 temperature, and the curves were drawn freehand with 

 the greatest care through them. By finding the locus of 

 the middle points of parallel chords, Mr. Dickson proved 

 that the cur\'es were all, with one exception, parabolas. 

 The exception was in the case of antimony-lead, for which 



NO. 2145, VOL. 85] 



the curve was a hyperbola. In the majority of cases the 

 parabolas differed from those obtained by Tait through 

 the more limited range of temperature used by him and 

 his students in the main fact that their axes were not 

 perpendicular to the temperature axis. The " Tait lines," 

 as it was convenient to name the lines of thermoelectric 

 power, were not in these straight, although limited por- 

 tions of them might be very nearly so. .As was easily 

 proved from the geometry of the parabola with inclined 

 axis, each Tait line was a curve with two asymptotes 

 perpendicular to one another. Of the metals investigated, 

 gold, silver, zinc, and German silver followed Tait's rule, 

 the thermoelectric powers referred to the lead line giving 

 straight lines ; but platinum, copper, cadmium, nickel, 

 manganese, palladium, and aluminium gave for their 

 electr<Mnotive-force curves parabolas with inclined axes. 

 Similar results were obtained from recent observations 

 published by Holborn and Wien, Barus, and from early 

 observations by J. Murray and J. C. Young, working 

 under Tait's directions. — Profs. -Alex. Smith and .A. W. C. 

 Menzies : A dynamic method for measuring vapour 

 pressures, with its application to benzene and ammonium 

 chloride. .A modified form of the isoteniscope, previously 

 described, was used in determining the vapour pressures 

 of these substances. The advantages of the new form of 

 apparatus were that it could be used for high pressures, 

 that the confining fluid could be reduced in amount, and 

 that the thermometer was inserted directly in the bath 

 with its bulb no longer in a region of varying pressure. — 

 Profs. Alex. Smith and W. C. IMenzies : A quantitative 

 study of the constitution of calomel vapour. The object 

 of the investigation was to find to what extent the vapour 

 of calomel was dissociated, and the method was to 

 measure the vapour pressures by means of the iscK 

 teniscope at various temperatures from 360° C. to 

 400° C. The results showed (i) that the vapour of 

 calomel was composed wholly of mercury and corrosive 

 sublimate, HgCl and HgCl being alike absent ; (2) that 

 calomel dissolves in mercury with a molecular weight 

 corresponding to the formula HgCl ; (3) that the isoteni- 

 scope may be used in the quantitative investigation of 

 chemical problems. — Dr. R. .A. Houston : The efficiency 

 of metallic filament lamps. The results were obtained by 

 means of a new method involving the examination with 

 a thermopile and ver\- sensitive galvanometer of the spec- 

 trum of the radiation transmitted by a water filter. The 

 values obtained for the efficiencies of carbon, osmium, 

 tantalum, and tungsten lamps as energy transformers were 

 respectively 29, 52, 6-5, and 75 per cent. 



Paris. 

 Academy of Sciences, November 21. — M. Emile Picard 

 in the chair. — H. Lorentz was elected a foreign associate 

 in the place of the late Prof. Schiaparelli. — Lord Avebury 

 was elected a correspondant for the section of anatomy 

 and zoology, in the place of Sir Ray Lankester, elected 

 foreign associate. — G. Fayet : The identity of the Cerulli 

 comet with the Faye comet. The elements calculated for 

 the two comets are nearly identical, the slight difference 

 noted being probably due to the fact that the considerable 

 disturbance of the orbit of the Faye comet caused by 

 Jupiter in 1899 was only approximately allowed for. — C. 

 Popovici : Observation of the Cerulli-Faye comet. Data 

 are given for November 22. — G. Tzitzeica : .A theorem of 

 M. Darboux. — W. SteklofT : A new application of the 

 method of development of fundamental functions. — Paul 

 L6vy : The integrabilit>- of the equations defining line 

 functions. — G. Eiffel : The resistance of rectangular planes 

 struck obliquely by the wind. Experiments were carried 

 out with a suction fan, using a 70 horse-power motor, 

 giving an air current of 10 to 20 metres per second in a 

 tube of 1-5 metres diameter. The results are given 

 graphically in a series of curves. — ^Jean Becquerel : The 

 reversal of the phosphorescence bands. Rubies and an 

 emerald were used for these experiments at the temperature 

 of liquid air. The reversal establishes a qualitative rela- 

 tion betw-een the emission and absorption, and some 

 quantitative relations are worked out. — R. Jouaust : The 

 magnetic properties of iron at high frequencies. The iron 

 was used in sheet form, the alternating current, produced 

 by a Poulsen arc, having a frequency of 150,000 per 



