December 23, 1922] 



NA TURE 



863 



w, vt>i an invariant theory can be constructed. This 

 theory has been studied principally by Peano, Kasner, 

 and Forsyth, but only for values oi m, n, not exceed- 

 ing 2. The present paper is preparatory to a proof 

 of Gordan's theorem — that the complete invariant 

 system of the (m, n) form is finite. It is the algebraic 

 theory answering to geometrical inversion. 



Paris. 

 Academy of Sciences, November 27. — M. Emile 

 Bertin in the chair. — Marcel Brillouin : Einsteinian 

 gravitation. Statics. Singular points. The material 

 point. Various remarks. — E. Fournier : Experi- 

 ments on the guidance of dirigible balloons through 

 fog by the method of W. A. Loth : their consequences. 

 The electrical method of M. Loth, originally designed 

 for the guidance of ships into port in foggy weather, 

 is equally applicable to aeroplanes and balloons. The 

 guiding cable may be either aerial or buried in the 

 earth. The latter method might be employed in 

 establishing aerial communications across the Sahara. 

 — L. Guignard : The existence of certain proteid 

 bodies in the pollen of various Asclepiadaceae. — 

 Charles Richet and Mme. A. G. Le Ber : Studies on 

 lactic fermentation. The action of very small doses 

 of substances apparently inoffensive. Substances 

 such as urea or milk, not considered poisonous, can 

 exercise, even at very great dilutions, a distinct 

 influence on the activity of the lactic ferment. It 

 follows that bacteria, since they react to such slight 

 influences, are never found under identical conditions 

 of development. — A. de Gramont : Ultimate lines 

 and spectral series. — P. Fatou : Certain uniform 

 functions of two variables. — Spyridion Sarantopoulos : 

 The number of roots of holomorphous functions in a 

 given curve. — Alf. Guldberg : Mean values. — Jacques 

 Rueff : Theory of the phenomena of exchange. 

 Two principles are enunciated giving the relations 

 between rates of exchange and purchasing power of 

 money in different countries, excluding countries 

 practising continuous inflation. The principles are 

 verified by constructing curves of the purchasing 

 power of the franc in England, the United States, 

 Italy, and Spain, over a series of years. — A. Buhl : 

 The secular movement of the perihelion of Mercury. — 

 Rodolphe Soreau : The laws of variation with alti- 

 tude, in the troposphere, of the characteristics of 

 standard air. — Henri Fabre : Hovering flight in the 

 Mediterranean. The flight of a bird (probably the 

 puffin) has been studied ; it rarely flies in calm 

 weather, and when forced to do so its flight resembles 

 that of a duck. But as soon as' the wind velocity 

 and height of the waves reach certain definite values, 

 the bird flies with motionless wings. The explanation 

 of this flight is based on the hypothesis that vertical 

 air-currents are produced by the wind striking the 

 waves. There must be both ascending and descend- 

 ing air -currents, but the bird utilises only those 

 ascending currents the direction of which is controlled 

 by the direction of the crests of the waves. — W. D. 

 MacMillan : Can the mean density of the Universe 

 be finite ? — Emile Borel : Remarks on the preceding 

 communication. — Ch. Maurain and Mme. de Madinhac: 

 Evaluation of the intensity of the vertical electric 

 currents traversing the soil in France. — R. Boulouch : 

 The aplanatic telescope. — R. Jouaust : The applica- 

 tion of pyrometers to high frequency measurements. 

 The Fery pyrometer can be utilised in some 

 measurements necessary in radiotelegraphic installa- 

 tions. Two examples are given, the calibration of 

 high frequency ammeters and the measurement under 

 working conditions of the resistance of the oscillating 

 circuit of a lamp generating station. — L. Gaumont : 

 A new sound amplifier. The vibrating part of this 

 apparatus consists of a silk cone on which is coiled 



NO. 2773, VOL. I 10] 



a spiral of fine aluminium wire ; the cone is fitted 

 between the poles of an electromagnet, similarly 

 shaped. The telephone currents pass round the 

 spiral wire on the cone, which is set in vibration by 

 the action of the magnetic field. The sound is 

 magnified without distortion, and one apparatus had 

 a range of hearing of 300 metres. — P. Lemay and L. 

 Jaloustre : Some microbiological consequences of the 

 oxidising properties of thorium-X. Earlier researches 

 showed that the radioactive elements behave as 

 oxidising catalysts. Tins suggested that thorium-X 

 should favour the growth of aerobic organisms and 

 slow down the development of anaerobic organisms. 

 Experimental proof of the correctness of this view 

 has been obtained, using B. lacticus and B. butyricus 

 as the test organisms. — P. Loisel and Michailesco : 

 The radioactivity of the springs of the Baths of 

 Hercules in Roumania. The waters from four of 

 seven springs examined show marked radioactivity, 

 in amounts varying with date of collection. — Leon 

 Guillet and Marcel Ballay : The vapour pressure of 

 some copper-zinc alloys in the solid state. The 

 vapour pressure of zinc in brass (zinc 44-8 per cent.) 

 varied between 3-0 mm. at 535° C. and 19-32 mm. at 

 630 C. In the presence of air, the loss of zinc was 

 smaller than in nitrogen, hydrogen, or carbon 

 monoxide. — MM. Dervin and Olmer : Ammoniacal 

 silver fluoride. This compound has the composition 

 AgF.2NH3.2H2O. On careful heating it loses 

 water, ammonia, and ammonium fluoride, leaving an 

 explosive nitride, Ag 3 N. — J. Valentin : The solidifica- 

 tion of the system MgCl 2 . KCI . BaCl 2 .— Paul Pascal : 

 Magnetic analysis of the stannic acids. Measure- 

 ments of the magnetic susceptibility of stannic oxide 

 in various states of hydration give no evidence of the 

 formation of any definite stannic acids. — F. W. 

 Klingstedt : The ultraviolet absorption spectra of 

 toluene and the xylenes. The three xylenes possess 

 very different absorption spectra. — Louis Grenet : A 

 possible modification of the iron-cementite diagram. — 

 L. J. Simon : The influence of the structure of 

 organic compounds on their oxidation by chromic and 

 sulphuric acids. The combustion of organic com- 

 pounds by the chromic-sulphuric acid mixture is not 

 always complete, and from the data given, there 

 would appear to be a relation between the amount of 

 carbon escaping combustion and the molecular 

 structure of the compound. — Andr6 Brochet : Some 

 properties of the active nickel employed as cata- 

 lyst in organic chemistry. — Marcel Delepine : The 

 iridio-dipyridino-tetrachlorides M[Ir(C 6 H 6 N) 2 Cl 4 ]. — 

 M. Faillebin : The hydrogenation of aldehydes and 

 ketones in the presence of pure and impure platinum 

 black. The reduction of aldehydes and ketones to 

 the corresponding alcohols by hydrogen with pure 

 platinum black as a catalyst gives bad yields : there 

 is a tendency for the formation of hydrocarbons, and 

 the catalyst becomes rapidly fatigued. If the 

 platinum black is made from a solution of chlor- 

 platinic acid containing ferric chloride, the impure 

 catalyst gives excellent yields of alcohols. — G. 

 Delepine and V. Milon : The presence of Waulsortian 

 reefs in the carboniferous limestone of the Laval 

 basin. — L. Barrabe : The presence of transferred 

 strata in the eastern Corbieres. — F. Roman : The 

 quaternary terraces of the upper valley of the Tagus. 

 — Albert Nodon : Researches on solar action at a 

 distance. — V. Schaffers : Lightning and trees. — E. 

 Roger : The periodic return of severe winters. In 

 i860 Renou noted that severe winters recur periodi- 

 cally. The author gives additional data in support 

 of this, and puts the period as 41 years. — E. Fichot : 

 The constitution of oceanic areas in basins of reson- 

 ance, originating from continental masses under the 

 action of the tides. — G. Hamel : Some peculiarities 



