May 3, 1900] 



NATURE 



23 



the candidates. Application forms may be obtained from the 

 secretary of the Technical Education Board, Ii6, St. Martin's 

 Place, W.C, to whom they should be returned not later than 

 May 14. The board is also offering scholarships for the en- 

 couragement of horticulture and gardening. Two of these, 

 tenable at the Swanley Horticultural College, Kent, give free 

 board and tuition for two years, and may be reckoned as of the 

 value of 60/. a year. They are open to candidates between the 

 ages of sixteen and twenty, and one will be awarded to a young 

 man and the other to a young woman as the result of a com- 

 petitive examination. No candidate is eligible whose parents 

 are in receipt of more than 400/. a year. 



SOCIIiT/ES AND ACADEMIES. 

 London. 

 Physical Society. — Ordinary meeting held by the invita- 

 lian of Sir Norman Lockyer, F.R.S., in the Solar Physics 

 Observatory, South Kensington, on April 27. — Mr. T. H. 

 Blakesley, Vice-President, in the chair.— Sir Norman Lockyer 

 gave a short account of the physical problems now being in- 

 vestigated at the Solar Physics Observatory, and their astro- 

 nomical applications. The chief work carried on at the 

 observatory is the comparison of stellar spectra with spectra 

 obtained from lights emitted by laboratory sources. The light 

 from a star (or the sun) and from an arc (or a spark) are 

 focussed alternately upon the slit of a spectroscope, and the two 

 spectra are photographed side by side upon the saAie plate. The 

 number of lines in the arc spectrum depends upon which part of 

 the arc is focussed on the slit. The image of the centre is rich 

 in lines, the image of the edge gives a few single lines. Changes 

 in spectra are also dealt with. The thickening and thinning of 

 lines depends upon several things. In the first place, it depends 

 upon the density of the substance, and thus the hydrogen lines 

 in the spectrum of Sirius are much broader than those in a Cygni, 

 the hydrogen being denser in the former star. Changes may 

 also be produced by variations in quantity. A reduction in the 

 quantity of a substance generally simplifies its spectrum, the 

 longest line disappearing last. The motion of a luminous body 

 to or from the spectroscope alters the wave-length of the light 

 emitted and produces a shift in the lines of the spectrum. The 

 amount of deviation is a measure of the velocity in the line of sight. 

 In the case of Nova Aurigce, we have dark and bright lines of 

 the same substance side by side. This shows that there are two 

 bodies involved, moving with different velocities, the one giving 

 a radiation and the other an absorption spectrum. Another 

 change in the lines depends upon temperature. In general an 

 increase in temperature produces a greater number of lines, a 

 notable exception being sodium, which gives its full number of 

 lines at the temperature of an ordinary Bunsen flame. The 

 spectra of metals obtained from the arc, and by sparking, are 

 often quite different. Those lines which make their appear- 

 ance, or are intensified in passing from the arc to the tiigher 

 temperature of the spark, are known as enhanced lines. The 

 '-omparison of stellar spectra with laboratory spectra is often easy. 

 r instance, the presence of iron in the sun and hydrogen in 

 lius is easily seen. Several lines in the spectrum of Bella- 

 lix have been shown to be due to helium, the position of the 

 lines being exactly the same as those due to the gases from 

 clevite. In many cases it is possible to build up the spectrum 

 of a star from the spectra of its constituents taken at the proper 

 temperatures. For instance, the spectrum of 7 Orionis can be 

 closely imitated by means of oxygen, nitrogen, and carbon 

 together with the well-marked lines of hydrogen and helium. 

 We can roughly estimate by the character of the spectra of stars, 

 the temperatures of those stars, and thus arrive at a stellar 

 thermometry. Starting with a hot star like Bellatrix, and pass- 

 ing through j3 Persei, 7 Lyra;, Sirius, Castor, Procyon to Arc- 

 turus, a cold star, we have a gradual change in the character of 

 the lines which appear in the spectrum of any constituent. The 

 widening of the lines in the case of spectra of sun spots enables 

 us to trace changes in temperature of the sun, and we can com- 

 pare these temperature changes with a variety of terrestrial 

 phenomena, such as variation in latitude. The extraordinary 

 number of lines exhibited by many metals suggests that what 

 we are accustomed to call chemical elements are really complex 

 bodies which are made up of simpler ones. Attempts have 

 been made to build up the spectra of metals by superimposing 



NO. T592, vol. 62] 



simple sets of lines upon one another. In many cases a great 

 number of series would be required to represent things com- 

 pletely. In the case of hydrogen it would be necessary to have 

 at least twenty-seven series to give the structure spectrum only. 

 Taking the atomic weight of hydrogen as unity, the atomic 

 weight of the little masses which might give rise to any one of 

 these series would be about -0019. This is of the order of mag- 

 nitude of the small bodies, of which the existence has been 

 suggested by Prof. J. J. Thomson from his work on ions. 



Paris. 

 Academy of Sciences. — M. Maurice Levy in the chair. — • 

 The President armounced to the Academy the death of M. 

 Alphonse Milne- Edwards, and gave an account of his work.^ 

 On linear partial differential equations of the second order, 

 and on the generalisation of the problem of Dirichlet, by M. 

 Emile Picard. — On the heats of combustion and formation of 

 some iodine compounds, by M. Berthelot. A redetermination . 

 of the heats of combustion of fourteen typical iodine derivatives. 

 In spite of preconceived notions to the contrary derived from 

 the incomplete combustion of such compounds as iodoform in air, 

 no difliculty was experienced in completely burning any of the 

 substances in the calorimetric bomb. — On rifling in cannon, by 

 M. Vallier. A discussion on the best form of curve for the rifling 

 of cannon, and an extension of the work of M. Zaboudski upon 

 the same subject. — On the upright trunks, stems and roots of 

 Sigillaria, by M. Grand'Eury. A study of^ the Sigillaria 

 existing in a quarry in the neighbourhood of St. Etienne. From 

 the fact that the stems {Syringodendron) ionnd in a vertical posi- 

 tion are not distributed at random, but are usually found in groups 

 near each other forming well marked colonies, and from other 

 characters of their growth, the author concludes that the hypo- 

 thesis of R. P. Schmitt that they have been transported by 

 water and deposited in the position found, is untenable. The 

 view of Dawson that they have grown upon unsubmerged soil is 

 also held to be untenable, all the facts noted by the author 

 pointing to the Sigillaria have grown in the place in which they 

 are found in marshy soil ; under water varying from i metre to 

 7 or 8 metres in exceptional cases. — Reply to a reclamation of 

 priority of M. Curie, by M. Gustave le Bon. — Reply by M. Th. 

 Tommasina to a reclamation of priority, by MM. Ducretet and 

 Popof. — Note by M. L. M. Bullier replying to M. Geelmuyden 

 on a question of priority. — On the complementary terms in the 

 criterium of Tisserand, by M. Gruey. — On differential equations 

 of any order whatever with fixed critical points, by M. Paul 

 Painlevc; — On the generalisation of analytical prolongation, 

 by M. Emile Borel. — The theoretical cycle of gas engines, 

 by M. A. Witz. A discussion of the remarks and 

 criticism of M. Marchis. — On the dielectric constant and 

 the dispersion of ice for electromagnetic radiations, by M. 

 C. Gutton. The value of the refractive index for electromagnetic 

 waves was found to vary with the wave-length from 176 for a 

 wave-length of 14 cm. to I'SO for 2088 cm., ice thus presenting 

 normal dispersion for electromagnetic waves. — Two applications 

 of Govi's camera lucida, by M. A. Lafay.— On the maximum 

 sensitiveness practically employed in coherers for wireless tele- 

 graphy, by MM. A. Blondel and G. Dobkevitch. The increase 

 of sensibility observed by M. Tissot to occur when the coherer 

 is placed in a magnetic field, is ascribed by the authors to purely 

 mechanical causes, the increase of contact between the powder 

 and the electrodes produced by their mutual attraction. — On the 

 radiations of radium, by M. E. Dorn. The author draws at- 

 tention to the fact that he published a note on the deviation of 

 the rays emitted by radioactive barium bromide in an electric 

 field on March II, independently of M. Becquerel. — On a new 

 thermo-calorimeter, by M. G. Massol. Two improvements on 

 Regnault's thermo-calorimeter are suggested, the replacement 

 of alcohol by sulphuric acid, giving a large increase in the range 

 of the instrument, and the use of a reservoir at the upper 

 end of the instrument as in Walferdin's maximum thermometer 

 by which the sensitiveness of the thermo-calorimeter is increased 

 without undue lengthening of the stem. The instrument thus 

 modified has been of especial service in the study of superfused 

 liquids. — A new indicator in acidimetry, and its application to 

 the estimation of boric acid, by M. Jules Wolff. The indicator 

 proposed is a solution of ferric salicylate in sodium salicylate, 

 which passes from violet to orange when the solutions become 

 alkaline. Data are given showing the results obtainable with 

 borates. — On the selenides and chloroselenides of lead, by M. 

 Fonzes-Diacon. — Crystallised lead selertide, PbSe, is obtained by 



