June 26, 19 19] 



NATURE 



339 



gauged without some considerable knowledge of the 

 various physico-chemical equilibria within the masses 

 at various stages of the general cooling process," the 

 author proceeds to enunciate four leading principles 

 as laid down by Le Chatelier, van't Hoff, Ostwald, 

 and Henry as a basis for calculating the general 

 characters and directions of the chemical changes 

 occurring during the cooling. He then deals with the 

 volume relationships of minerals and the problem of 

 volcanic power, the evolution of igneous rocks bv 

 magmatic differentiation, and the formation and 

 behaviour of submagmas, from which he goes on to 

 classify igneous-ore deposits under three types, namely, 

 those due to precipitation concentration, solution con- 

 centration, and a third group which appears to arise 

 from the degasification of enriched subsidiary magmatic 

 differentiates, this latter class not improbably includ- 

 ing the metallic copper of the Lake "Superior region 

 and the gold deposits of the Rand. The author's 

 endeavour is, however, rather to illustrate a method 

 of attack on some of the problems than to discuss in 

 detail any particular deposits, and he urges a more 

 extended practice of what he terms magmatic geologv 

 as a means to that end. 



Edinburgh. 

 Royal Society, June 2.— Dr. John Home, president, 

 in the chair.— Dr. L. Dobbin : The presence of formic 

 acid in the stinging hairs of the nettle. The generally 

 accepted view that formic acid is present in the 

 stinging hairs of nettles is not convincingly estab- 

 lished by previous investigations in which nettles, as 

 a whole, and not exclusively the cell-contents of the 

 stinging hairs, were submitted to examination. The 

 author has secured the collection of these cell-contents 

 alone, and the conversion of the free acid or acids 

 which they contain into corresponding salts, by press- 

 ing the leaves of growing nettles between strips of 

 the purest filter-paper previously impregnated with 

 barium hydroxide or sodium carbonate and dried in 

 air. The optical characters of the lead and barium 

 salts prepared from the material so collected were 

 examined by aid of the polarising microscope, and 

 the various preparations were found to include crystals 

 possessing the same characters as known specimens 

 of lead formate and barium formate. — Dr. R. A. 

 Houstoun : X-ray optics. Part i. A method that the 

 author developed ten years ago for calculating the 

 number of electrons per molecule concerned in the 

 production of an absorption band is applied to absorp- 

 tion bands in the X-ray region. The mean result for 

 five " K" bands comes out 1002. This is at once a 

 verification by a new method of the wave-lengths in 

 the X-ray region, and a guarantee that the theory of 

 dispersion holds in this region. Other X-ray problems 

 are then treated.— Dr. A. C. Mitchell : Pulsations of 

 the vertical component of terrestrial magnetic force. 

 An account was given of observations recently made 

 at Eskdalemuir Observatory of pulsations in the 

 vertical component of the earth's magnetic force. 

 Although the ordinary recording magnetograph may 

 apparently register an undisturbed state of the earth's 

 magnetism, minute investigation by means of large 

 loops of cable laid over the ground shows that there 

 is continual agitation going on. This state of dis- 

 turbance is less noticeable during the night than 

 durinfj the dav; it takes peculiarly characteristic forms 

 during displays of the aurora ; v^hile the method of 

 observation is sufficiently delicate to observe oscilla- 

 tion periods as low as one-seventh of a second. These 

 very raoid oscillations are, it is believed, identical with 

 the fundamental period of the earth's oscillation as 

 an electrified sphere. Other sudden changes, such as 

 those which freauentlv usher in a magnetic storm, 

 can also be studied in detail by this method.— Col. 

 NO. 2591, VOL. IO3I 



R. A. Marr <iNorfolk, Virginia, U.S.A.) : Samples of 

 encysted wood. This wood, obtained from the Balsa 

 tree, is extremely light, its density being about half 

 that of cork. Unfortunately, it rotted easily in its 

 natural state, but by a special process discovered by 

 the author a waterproofing mixture could be carried 

 to the centre of any piece of timber, coating the cells 

 and ducts with an extremely thin permanent film. In 

 this form the wood had been of great service in 

 floating mines during the war. 



j Paris. 



Academy of Sciences, June 2.— M. L6on Guignard in 

 I the chair.— E. Picard, B. Baillaud, and M. Ferrid : A 



I project of the Bureau des Longitudes relating to the 

 determination of a network of longitudes and latitudes 

 all over the world. Three points are suggested : Paris, 

 Shanghai, and near San Francisco. The differences 

 of longitude are to be determined by comparisons 

 between pendulums using wireless signals. The pre- 

 cision attainable should be of the order of 001 sec. of 

 time. Greenwich and a point in Nev^ Zealand are 

 suggested as additional points on the chain. — H. 

 Deslandres : Observations relating to the total eclipse 

 of the sun on May 29, made at the Meudon Observa- 

 tory. The eclipse was not visible at Meudon, and it 

 did not prove possible to organise an expedition on 

 account of war conditions. Observations of an un- 

 usually large prominence were made. Experiments 

 on wireless communication with the Island of Ascen- 

 sion were also made; the signals from this station 

 are not usually perceived during the daytime, but at 

 the moment the umbra and penumbra of the moon 

 produced a weakening of the normal illumination on 

 that portion of the earth between Ascension and 

 France the signals were clearly made out.^ — G. 

 Bigourdan : The unification of astronomical and civil 

 time. It has been agreed between the United States, 

 Great Britain, and France that, commencing January i, 

 1925, the astronomical day shall commence, like the 

 civil day, at midnight. — M, Tilho : A scientific expedi- 

 tion of the Institute of France in Central Africa. 

 Geographical sketch of the Tibesti, Borkou, and 

 Ennedi. — M. Emile Bourquelot was elected a member 

 of the section of chemistry in succession to the late 

 M. Jungfleisch. — G. Julia : Integral functions and 

 growth. — E. Kogbetliantz : The summation of divergent 

 series. — J. Rey : The flow of petrol vapour.^ — P. Fox : 

 Measurements of stellar parallax at the Dearborn 

 Observatory. Data for thirty-five stars are given, 

 obtained by the photographic method. The accuracy 

 is about 001 sec. — E. Belbt : New data on the primi- 

 tive solar nucleus, its encounter with the original 

 nebula, and the formation of spiral nebulae. — M. 

 Marti : A method of sounding at sea from a moving 

 vessel, based on the propagation of sound in water. 

 A small charge of explosive is detonated. A micro- 

 phone receives and records the original sound, and 

 then its echo, reflected off the sea-floor. The accuracy 

 of reading permits of detecting differences in depth to 

 about I metre, but the uncertainty of the mean tem- 

 perature of the water introduces an error of about 0-3 per 

 cent. — L. Dnnoyer : The error in dead-reckoning in- 

 volved by incomplete knowledge of the wind veloci- 

 ties. — H. Abraham and E. Bloch : The measurement in 

 absolute value of the periods of high-frequency oscilla- 

 tions. — M. Boll : The evolution of very dilute solutions 

 of tetrachloroplatinic acid in total darkness and at 

 varying temperatures.— G. Chavanne and L. J. Simon : 

 The critical solution temperatures in aniline of the 

 principal hydrocarbons contained in petrol. Seven- 

 i teen hydrocarbons were examined, and these were 

 I found to fall in three main groups : the aromatic 

 I hydrocarbons miscible at the ordinary temperature; 



