434 



NATURE 



[March i, 1900 



sounds were produced by electric sparks, and photographed by 

 means of the light emitted by carefully-timed subsequent sparks, 

 according to the methods described in the Phil. Mag. for last 

 year. The photographs included : {a) The reflection of a 

 spherical wave, as a spherical wave from a plane surface ; {b) 

 the reflection, by an ellipse, of circular waves from one focus, 

 and the concentration of the waves, as circular waves, at the 

 other focus ; (c) the plane wave-front formed by the reflection 

 of a spherical wave at a parabolic surface ; (r/) the wave-front 

 formed by a spherical wave incident on a spherical surface ; {e) 

 the wave-front formed by a plane wave incident on a spherical 

 surface. In cases {d) and (e) the wave-fronts are complicated, 

 and contain cusps. Prof. Wood pointed out that the paths 

 of the cusps on the wave-fronts traced out the caustic curves. 

 In the following cases the wave-fronts were drawn for one 

 hundred successive positions, and the evolution of the reflected 

 wave was made clear by means of a kinematograph : (a) Plane 

 wave on a hemispherical mirror ; {b) spherical wave on a hemi- 

 spherical mirror ; and (tr) circular wave inside a complete circular 

 mirror. (2) A new seudoscope. In this instrument the real 

 and inverted images formed by two convex lenses are viewed 

 stereoscopically. The inversion of the object viewed causes the 

 relief to be reversed. (3) Diff"raction colour-photographs. 

 Prof. Wood showed some coloured photographs taken by his 

 diffraction process. The principle of the method is based upon 

 the tri-colour theory. Different colours are produced by 

 gratings so ruled and arranged as to throw upon the eye the 

 particular constituents of the required colours. The arrange- 

 ment of gratings necessary to produce a coloured picture is 

 obtained by photographing properly spaced gratings through 

 red, green and blue chromograms of the object. The super- 

 position of one grating upon another which occurs in this pro- 

 cess gives rise to an in-and-outof-step arrangement, which pro- 

 duces secondary spectra. These, however, seldom affect the 

 picture to any serious extent. (4) Artificial parhelia. When 

 printing fine gratings upon gelatine, if the film is too thick, no 

 print is formed, but the gelatine warps. If such a film is placed 

 in a converging beam, the central image is accompanied by four 

 marked concentrations of light situated at the extremities of 

 two diameters at right angles. An examination of one of these 

 plates with a microscope shows that there is a ridge for every 

 third line of the grating, and that the plate is crossed at right 

 angles to these lines by irregularly spaced cross ridges. Prof. 

 Wood also exhibited some photographs taken by zone plates, 

 a silvered copy of a Rowland grating, a photograph of a 

 dynamite explosion, the motion of a ball in its flight, and the 

 anomalous dispersion produced by a cyanine prism. — Mr. Boys 

 gave some details concerning the photograph of the explosion 

 shown. — Prof. Everett expressed his interest in the demonstra- 

 tions. — Prof. Herschel asked if the photographs of sound waves 

 after reflection had been verified by comparison with waves on 

 mercury. — Mr. Watson pointed out that this could not be done, 

 as it is impossible to get a solitary wave on the surface of 

 mercury. Owing to the dependence of velocity on wave-length, 

 any such solitary wave draws out into a train of waves.— The 

 chairman proposed a vole of thanks to Prof. Wood, and an- 

 nounced that, by invitation of Prof. Callendar, a special meeting 

 will be held at University College on March 2. — The meeting 

 then adjourned. 



Chemical Society, February 8. — Sir Henry Roscoe, Vice- 

 President, in the chair. — Prof. T. E. Thorpe, President, de- 

 livered the Victor Meyer Memorial Lecture. — February 15, 

 Prof. Thorpe, President, in the chair. — The following papers 

 were read. — Ammonium amidosulphite, by E. Divers and 

 Masataka Ogawa. Dry ammonia and sulphur dioxide do not 

 combine at a low temperature, but on passing sulphur dioxide 

 into a dry ethereal ammonia solution, a colourless, deliquescent 

 unstable salt, ammonium amidosulphite, NH4.SO2.NH2, is 

 deposited ; it is decomposed by water and dissolves in alcohol, 

 with formation of ethyl ammonium sulphite. — On the products 

 obtained by heating ammonium sulphites, thioiulphate and 

 trithionate, by E. Divers and Masataka Ogawa. Anhydrous 

 ammonium sulphite and pyrosulphite sublime unchanged on 

 heating in dry nitrogen. — The colour of alkali nitrites, by E. 

 Divers. The author confirms his previous statement that the 

 alkali nitrites have a .slight yellow colour which is specially 

 marked in solution. — Solubility of mixed potassium nitrite and 

 nitrate, by E. Divers. — The combination of sulphur dioxide 

 with oxygen, by E. J. Russell and N. Smith. When a mixture 

 of sulphur dioxide and oxygen acts on certain oxides, in 



NO. 1583, VOL. 61] 



addition to the absorption of sulphur dioxide, sulphur trioxide is 

 formed, owing apparently to the "surface action " of the oxide ; 

 no sulphur trioxide is formed unless a simultaneous absorption 

 of sulphur dioxide occurs. — Notes on the estimation of gaseous 

 compounds of sulphur, by E. J. Russell. Volumetric methods 

 of analysis are given which work satisfactorily in the estimation 

 of sulphur dioxide, hydrogen sulphide, carbonyl sulphide and 

 carbon disulphide in gaseous mixtures. — The influence of the 

 "nascent state " on the combination of dry carbon monoxide 

 and oxygen, by E. J. Russell. The nascent condition has no 

 great effect in promoting combination between carbon monoxide 

 and oxygen, the unburnt residue of carbon monoxide being 

 similar in amount to that found in Dixon's experiments ; the 

 sources of nascent carbon monoxide used were carbonyl sulphide 

 and nickel carbonyl, whilst nascent oxygen was supplied by the 

 monoxide and peroxide of chlorine. — Asymmetric optically 

 active tin compounds. Dextromethylethyl-n-propyl tin iodide. 

 Preliminary note, by W. J. Pope and S, J. Peachey. The 

 previously unknown mixed alkyl tin compounds of the type 

 SnX'X"X">X'^ can be readily prepared from trimethyl tin iodide 

 by the following series of reactions : 



( 1 ) 2SnMe3l + ZnEt.2 = 2SnMe3Et + Znlg. 



(2) SnMe3Et-fl2 = SnMe2EtI-f-MeI. 



(3) 2SnMeoEtI -f ZnPrg = aSnMe.^EtPr ■\- Znlg. 



(4) SnMejEtPr -t- 13= SnMeEtPrI -f Mel. 



On treating methylethylpropyl tin iodide with silver dextro- 

 camphorsulphonate, it yields dextromethylethylpropyl tin 

 dextrocamphorsulphonate, SnMeEtPr(C]oHi50S03), from the 

 aqueous solution of which dextromethylethyl-n-propyl tin iodide 

 may be precipitated by potassium iodide. — Note on the ••efraction 

 and magnetic rotation of hexamethylene, by S. Young and 



E. C. Fortey. — Apiin and apigenin. Part II. Note on 

 vitexin, by A. G. Perkin. — The yellow colouring principles of 

 various tannin matters, VII., by A G. Perkin. — Note on the 

 bromo-derivatives of camphopyric acid, by J. A. Gardner. 

 Camphopyric acid yields two derivatives, o- and 0-bromo- 

 camphopyric acid, with bromine ; the former gives an 

 a-hydroxycamphopyric acid, C9Hi3(OH)04, on hydrolysis with 

 potash. 



Mathematical Society, February 8.— Prof. Elliott, V.P., 



F. R.S., and subsequently Lieut. -Colonel Cunningham, V.P., 

 in the chair.— Prof. Elliott announced that the Council had 

 passed the following resolution, and registered the same at 

 Somerset House, viz. that the objects of the Society requiring 

 that it shall consist of more than 250 members, it is resolved 

 that the number of its members may be increased by further 

 elections to 350. —Prof. Love, F.R.S., communicated a paper, 

 by Mr. J. H. Mitchell, on some elementary distributions of 

 stress in three dimensions, and Major MacMahon, F.R.S., 

 gave a sketch of further results arrived at by him in combina- 

 torial analysis, the foundation of a new theory. — The following 

 papers were taken as read, viz. : A formula in the theory of 

 the theta functions, by Prof. A. C. Dixon ; The canonical 

 reduction of a pair of bilinear forms, and Reduction of a 

 generalised linear substitution to a canonical form, with a 

 dynamical application, by Mr. Bromwich. 



Anthropological Institute, February 13. — Mr. C. H. 

 Read, President, in the chair.— Mr. W. L. H. Duckworth 

 presented a note on the Congress of German and Viennese 

 anthropological societies held at Lindau in September 1899, 

 and on the anthropological faculty lately established in the 

 University of Munich.— Dr. R. Koettlity gave a detailed 

 description of the ethnography and civilisation of the Somali, 

 Galla, Abyssinian, and Shangalla tribes, which he had the 

 opportunity of studyiug during a recent journey from the Gulf 

 of Aden to Khartoum. The paper was illustrated by many 

 lantern slides from sketches and photographs, and by a large 

 number of specimens collected in the course of the expedition — 

 In the discussion which followed, Mr. E. G. Ravenstein laid 

 great stress upon the importance of a careful and detailed study 

 of the natives of the region in question, and especially of the 

 southern Galla tribes, who remain practically uninfluenced 

 either by the Mohammedanism of the coast or by the debased 

 Christianity of the Abyssinians in the interior. 



Royal Meteorological Society, February 21.— Mr. E, 

 Mawley read his report on the phenological observations for 

 last year, in which he showed that the weather for the year 

 ending November 1899 was chiefly remarkable for its high 



