62 



NA TURE 



[November 15, 1894 



he detection of extremely delicate differences in density, Mr. 

 Anderson satisfied himself that capillarity has no perceptible effect 

 upon the accuracy of the readings. By a series of observations 

 at different temperatures he has been able to construct new tables 

 for the reduction of observed densities to standard temperature, 

 and for the calculation of the function D, which is the difference 

 of density between the sample and pure water divided by the 

 number of grammes of chlorine per litre, a function to which 

 considerable importance is now attached in the discussion of the 

 relative differences between samples of sea-water. 



Our excellent contemporary, The Engineering Magazine, 

 commenced a "Review of the Industrial Press" in the October 

 number, andanindexof current technical literature. The object 

 of this review and index is to give concisely-written notices of the 

 most important articles of the month ; and to supply a carefully 

 classified index to all the articles published currently in the 

 scientific and industrial press of the United States and Great 

 Britain. An entirely new feature is the establishment of a 

 department to supply all or any portion of any article reviewed 

 or indexed. That technical journalism has grown to pro- 

 portions and importance which warrant such a development, is 

 a fact at which we can all rejoice. 



Observations on the variations in level of well-water have 

 been made for the last three years at the Observatory of Catania 

 in Sicily, and the first results are described in a paper by 

 A. Ricci) and S. Arcidiacono (Boll. mens, delf Ace. Cioenia di 

 Sei. Nat. in Catania, fasc. 37, June 10, 1894.) They classify 

 the movements into progressive, annual and accidental, sub- 

 dividing the la'.ter into meteoric and geodynamic. The 

 accidental variations of geodynamic origin consist of small 

 abrupt changes of level, generally downwards, which frequently 

 correspond to movements of the ground. Shortly before the 

 eruption of Etna in 1892, and for several months after, the 

 changes in level of the water-surface were extremely irregular. 

 From June I, to December 31, 1892, corresponding to]thirly-nine 

 groups of earthquakes, there were abrupt changes of level within 

 twenty-four hours in twenty-one cases ; there were also fifty small 

 but marked changes coinciding with strong oscillations of the 

 tromometer. Somewhat similar observations have been made 

 in Wisconsin, by Prof. F. H. King (U. S. Dep. of Agri. 

 Weather Bureau, Bull. No. 5). Here the shock was imparted 

 by heavily-laden trains passing less than fifty yards from the 

 well ; but the surface of the water invariably rose, sometimes 

 as much as one tenth of an inch, returning to its former level 

 after a few seconds. 



At a recent meeting of the Academy of Science of Amstec- 

 dam, Herr C. H. Wind read a note on the Kerr phenomenon. 

 Th;: author breaks up the clsclric current into two parts — a 

 current of conduction and a displacement current — and to these 

 attributes, as Lorentz has done, the Hall effect. He supposes, 

 however, that the electromotive force which constitutes the Hall 

 effect is different for the two constituents, while Lorentz sup- 

 poses them to be equal. The introduction of this hypothesis 

 into the calculations of Van Loghem does not alter the general 

 form of the results, but has the effect of giving expressions for 

 the phase and the amplitude of the magncto-op'.ic component 

 which differ by a constant quantity and a constant angle from 

 the old values. In this way the difference of phase discovered 

 by S.ssingh it explained ; and from the observed value of this 

 difference of phase the ratio Iwtween the intensity of the Hall 

 effect for the displacement and conduction currents can be cal- 

 cula'ed, and then from observations of the amplitude the value 

 of each of these can be found. From the calculations made 

 by the author, it appears that the values thus obtained are of 

 NO. 1307. VOL. 51] 



the same order as those got by direct observation of the Hall 

 effect, if we suppose that the specific resistance of metals for 

 periodic currents of extreme rapidity is greater than for con- 

 tinuous currents. This view is further supported by other cal- 

 culations which have been made by the author. The paper 

 concludes with a comparison between the above theory and the 

 theories propounded by Thomson, Goldhammer, and Drude, 



I.N" No. 38 of the Silztingshriihte of the Berlin .\cademy, 

 Prof. Goldstein gives an account of a curious effect which the 

 cathode rays exert on the colour of certain salts. If potassium 

 chloride be made to phosphoresce in a radiation-tube, it quickly 

 assumes a strong heliotrope shade, and eventually becomes 

 bright violet. On heating, the colour changes to blue, and at 

 high temperatures the salt becomes white. The same series of 

 colour-changes may be obtained with this decolourised salt, 

 and also with naturally occurring pot-issium chloride or sylvine. 

 Several haloid salts of the alkali metals were examined, and 

 with the exception of c.^ciium and rubidium chlorides all gave 

 after-colours. The chlorides of barium and strontium gave no 

 after-colours. In ordinary air the colour disappears the more 

 quickly the more soluble the salt. The colour of lithium 

 chloride fades almost immediately ; the blue colour of sodium 

 chloride lasts about a day. In contact with water the salts at 

 once lose their colour. In a vacuum or in dry air the deep blue 

 colour of lithium chloride has now lasted for two months with- 

 out apparent change. The colour of potassium chloride 

 gradually fades and completely disappears in ,-ibout a week ; the 

 behaviour of mosi of the salts is like that of potassium chloride. 

 The cause of these phenomena is unknown The salts were as 

 pure as could be obtained. Electrodes of different materials 

 gave the same results. The radiation-tubes contained, of 

 course, a little mercury vapour, but none of the kno.vn com- 

 pounds of mercury with the constituents of the salts have the 

 colours above described. Chemical decomposition is unlikely, 

 since the coloured salt gradually changes into its original con- 

 dition. The author inclines to the view that during phosphor- 

 escence the particles of the salt have been m.ide to take up 

 positions and motions di:Tering from those of the unaltered 

 substance, and that a physical modification of the salt has thus 

 been brought about. 



Some efforts have again been made in France to overcome 

 the air resistance which a locomotive encounters when running 

 at a high rate of speed. La Nature, for October 27, contains 

 a very interesting article by M. .Max de Nansouty, descriptive of 

 the experiment; of M. Kicour, originally made in 1887. In 

 these, inclined planes were placed in front of the engine, and 

 by adopting this means, making the slanting planes four in 

 three, and filling up the spokes of the wheels, the resistance 

 was diminished by one half. This resulted in a notable in- 

 crease of useful work, and an economy of ten per cent, on the 

 coal consumption. The results are so satisfactory that M. 

 Ricourhas fitted his apparatus on forty engines belonging to the 

 Paris-Lyon-Mediterrance Railway, for general traffic. Similar 

 experiments were carried out in 1890 by M. Dresdouit, chief 

 engineer to the State railways, and they were of more prolonged 

 character. The engines in this case were ran 300,000 kilo- 

 metres, and by means of this apparatus they saved six to eight 

 per cent, in coal consumption, and sometimes as high as twelve 

 per cent. M. Max de Sonly tells us, however, "il est vrai que 

 le chauffeur et le mccanicien ctaient excel lents." A few other 

 experiments were tried with seemingly the same satisfactory re- 

 sults. The main poini, however, thai, on an average, a benefit 

 of four to five per cent, is obtained by the use of thesi inclined 

 planes, and it is asserted thit this is more than the saving 

 obtained from locomotives with compound and other systems. 

 If the statemen t be true, our locomotive superintendents had 



