4o8 



NATURE 



[August 23, 1900 



Or, if the gravitation is less in the crossed than in the parallel 

 position, and in constant ratio, the difference is less than i in 

 16,000 in the one case and less than i in 2800 in the other. 



We may compare with these numbers the difference of rate of 

 travel of yellow light through a quartz crystal along the axis and 

 perpendicular to it. That difference is of quite another order, 

 being about i in 170. 



As to other possible qualities of gravitation, I shall only 

 mention that quite indecisive experiments have been made to 

 seek for an alteration of mass on. chemical combination,^ and 

 that at present there is no reason to suppose that temperature 

 affects gravitation. Indeed, as to temperature effect, the 

 agreement of weight methods and volume methods of measuring 

 expansion with rise of temperature is good, as far as it goes, in 

 showing that weight is independent of temperature. 



So while the experiments to determine G are converging on 

 the same value, the attempts to show that, under certain con- 

 ditions, it may not be constant, have resulted so far in failure all 

 along the line. No attack on gravitation has succeeded in 

 showing that it is related to anything but the masses of the at- 

 tracting and the attracted bodies. It appears to have no relation 

 to physical or chemical condition of the acting masses or to the 

 intervening medium. 



Perhaps we have been led astray by false analogies in some of 

 our questions. Some of the qualities we have sought and failed 

 to find, qualities which characterise electric and magnetic forces, 

 may be due to the polarity, the -f and - , which we ascribe to 

 poles and charges, and which have no counterpart in mass. 



But this unlikeness, this independence of gravitation of any 

 quality but mass, bars the way to any explanation of its nature. 



The dependence of electric forces on the medium, one of 

 Faraday's grand discoveries for ever associated with the Royal 

 Institution, was the first step which led on to the electromagnetic 

 theory of light now so splendidly illustrated by Hertz's electro- 

 magnetic waves. The quantitative laws of electrolysis, again due 

 to Faraday, are leading, I believe, to the identification of elec- 

 trification and chemical separation, to the identification of 

 electric with chemical energy. 



But gravitation still stands alone. The isolation which Fara- 

 day sought to break down is still complete. Yet the work I have 

 been describing is not a failure. We at least know something in 

 knowing what qualities gravitation does not possess, and when 

 the time shall come for explanation all these laborious and, at 

 first sight, useless experiments will take their place in the 

 foundation on which that explanation will be built. 



SOCIETIES AND ACADEMIES. 



Paris. 



Academy of Sciences. August 13. — M. Maurice Le'vy in 

 the chair. — On the neogenic regions of Lower Egypt and the 

 Isthmus of Suez, by MM. C. Deperet and R. Fourtau. Of the 

 Miocene formation the following were recognised : — The Burdi- 

 galian, or first Mediterranean stratum, by the presence of 

 Echinolampas amplus, Scutella Inmsi, Lovenia, Cidaris 

 avenionensis, Amphiope truncata and other fossils ; the 

 Vindobonian, or second Mediterranean stratum, by a blue lime 

 containing Pecten cristato-costatus and numerous echinoderms. 

 Of the Pliocene, in the neighbourhood of Cairo, are layers of 

 yellowish sand containing Clypeaster aegyptiacus and other 

 characteristic fossils. — The area of the basins of Russia in Asia, 

 by M. J. de Schokalsky. The map is made upon the scale of 

 I in 4,200,000, and the area evaluated by means of a sheet of 

 celluloid divided in square millimetres. The area found is 

 16,085,000 sq. kilometres. — On a hypsometric map of 

 European Russia, by M. J. de Schokalsky. The previous map 

 of M. de Tillo was limited by the latitude 60° N. ; the present 

 map includes the whole of European Russia upon a scale of i 

 in 15,300,000. — Observations of the Borelly comet, made at the 

 Observatory of Algiers with the 31 "8 cm. equatorial, by M. F. 

 Sy.— A new arrangement of apparatus serving to measure geo- 

 desic bases, by M. Alphonse Berget. Ruled plates of iron float- 

 ing in a bath of mercury are used instead of the ordinary scales. 

 The method has the advantage of securing without trouble the 

 absolute horizontality of the rules ; two consecutive rules are 

 necessarily in the same horizontal plane, since their mercury 

 baths are connected ; there is no correction necessary for the 

 flexure of the rules, and the temperature correction is much 

 more certain. — Stereoscopic vision of curves traced by a phase 

 apparatus, by M. Marc Dechevrens. — Properties of magnetic 



i Landolt, 2«V. /?<> Phys. Chem., xii. i, 1894. Sanford and Ray, 

 Physical Review, v. 1897, p. 247. 



deposits obtained in a magnetic field, by M. Ch. Maurain. Iron 

 was deposited in a magnetic field either from a solution of ferrous 

 and ammonium chlorides, or from a solution of ferrous sulphate 

 in sodium pyrophosphate. It was found that the intensity of 

 magnetisation of different layers of the deposit growing in a 

 uniform field has the same value, and that the uniform mag- 

 netisation acquired by a depo.sited strip increases with the 

 strength of field in which the deposit is obtained. — The role of 

 discontinuities in the propagation of explosive phenomena, by 

 M. Paul Vieille. On the assumption of an adiabatic elasticity, 

 together with continuity, the velocities of wave propagation 

 found in certain cases are too great. It is necessary to assume 

 that the phenomenon is discontinuous. — Action of hydrogen 

 upon the sulphides of arsenic, by M. H. Pelabon. Details of 

 experiments of the interaction of realgar and hydrogen in sealed 

 tubes at 610° C. The reaction is a reversible one, and the limit 

 is affected by the introduction of an excess of arsenic. — 

 The properties of the blue oxide of molybdenum, by 

 M. Marcel Guichard. The blue oxide is a molybdate, and 

 could not be obtained free from water, two oxides of molybdenum 

 only existing in the anhydrous state, M0O2 ^"^ MoO.,. — On the 

 colouring matter of Echinus escu/entus, by M. Griffiths. — On 

 the composition of the ashes of some medicinal plants, by M. 

 Griffiths. — On a cause of error in the examination of wines for 

 salicylic acid, by M. J. Ferreira da Silva. The method of Petlet 

 and Grobert will indicate the presence of salicylic acid in a pure 

 wine that is really free from it. The official German method 

 gives exact results. — On a variety of the anthrax bacillus ; a 

 short asporogenic form. Bacillus anthracis brevigemvians, by 

 M. C. Phisalix. In the organism of the dog the B. anthracis 

 undergoes important modifications, becoming shorter with a 

 rapid and complete segmentation. It is still uncertain whether 

 this should be regarded as a variety or a new species. — Anti- 

 hepatic serum, by M. C. Delezenne. — Application to man of the 

 regeneration of confined air by means of sodium peroxide, by 

 MM. A. Desgrez and V. Balthazard. The apparatus described 

 weighs twelve kilograms, and by its means a man can penetrate 

 easily into an irrespirable atmosphere. 



CONTENTS. PAGE 



A Museum Catalogue 385 



A Text-book of Mammals. By R. L 386 



Good and Bad Air. ByJ. B. C. . . 387 



Our Book Shelf:— 



Le Dantec : " Lamarckiens et Darwiniens ; Discussion 

 de quelques Theories sur la Formation des 



Especes."— F. A. D 388 



" Helen Keller : Souvenir" 388 



Binet : " The Psychology of Reasoning " . ... 388 



" Electric Batteries : How to Make and Use Them" 388 

 Letters to the Editor: — 



Snowdrifts on Ingleborough in July. — Prof. T. 



McKenny Hughes, F.R.S 389 



The Total Eclipse of the Sun of May 17-18, 1901. 



—J. J. A. Muller 389 



The Reform of Mathematical Teaching. — David Mair 389 

 Functions of an Organ of the Larva of the Puss Moth. 



—Arthur S. Thorn 389 



Dark Images of Photographed Lightning Discharges. 



— J. B. Hannay 389 



The Lavoisier Monument. {Illustrated.) 390 



Nile Floods and Monsoon Rains 391 



The Forthcoming Meeting of the Britfsh Association 



at Bradford. By Ramsden Bacchus 392 



Notes 394 



Our Astronomical Column: — 



Velocities of Meteors 398 



Standards for Faint Stellar Magnitudes 398 



The Total Solar Eclipse, May 28, 1900 398 



Report of the Cape Observatory 398 



Rousdon Observatory (Devon) 398 



Independent Day Numbers for 1902 398 



The August Perseids of 1900. By W. F. Denning 398 

 What Pressure is dangerous on Electric Railways 



with Overhead Trolley Wires. By William Rung 399 

 Sea-coast Destruction and Littoral Drift. By 



W. H. Wheeler 400 



Recent Studies in Gravitation. {Illustrated.) By 



Prof. John H. Poynting, F.R.S 403 



Societies and Academies 408 



NO. 1608. VOL. 62] 



