September 29, 1898] 



NATURE 



533 



Thompson described and exhibited an experiment by Righi on 

 the production of the Zeenian phenomenon by absorption. A 

 beam of plane polarised white light is passed along the lines of 

 force of a magnetic field, and received in an analyser adjusted 

 to extinction with zero field ; in the magnetic field is a sodium 

 flame or a tube filled with nitric oxide. On setting up the field 

 a brilliant yellow light is seen, which cannot be extinguished by 

 rotating the analyser ; spectroscopic examination shows it to 

 consist of doubled sodium lines, the constituents of each doublet 

 being slightly more and slightly less refrangible respectively 

 than the original lines. In the case of nitric oxide the light 

 seen is bluish-green, being complementary to the colour of nitric 

 oxide by transmission, and the spectrum consists of doublets. 

 Profs. Lodge and Glazebrook thought that the phenomenon 

 might be fully explained by supposing the magnetic field to alter 

 the period of vibration of the ions so that they respond to waves 

 of slightly higher or lower frequency than their natural one. 

 Dr. C. E. Curry read a paper on the electromagnetic theory of 

 reflexion on the surface of crystals. 



A communication from Mr. J- Burke referred to the luminosity 

 produced by striking sugar. The rim of a rapidly revolving 

 disc of sugar is struck automatically by a hammer at the rate of 

 about two blows per second ; this causes an almost continuous 

 luminosity extending from the hammer inwards and downwards. 

 The spectrum of the light is confined to the more refrangible 

 side of the F line, and the nature and appearance of the 

 luminosity are unchanged by altering the medium surrounding 

 the sugar. No satisfactory explanation of the phenomenon has 

 yet been found. 



The report of the Electrical Standards Committee is a record 

 of progress made in the determination of the standard ampere. 

 Profs. Ayrton and J. V. Jones have designed an ampere balance, 

 for the construction of which a grant has been made by the 

 Association. The detail.? of the instrument were described to 

 the Section. An appendix to the report contains an account of 

 the determination of the temperature-coefficients of two coils 

 used in the determination of the ohm by Profs. Ayrton and 

 Jones, the measurements having been made by Mr. M. Solomon. 

 The coils do not appear to have changed since 1896, but their 

 resistances as mea.sured in 1894 were slightly lower (0006 to 

 0*007 per cent.) than the present values. The Electrolysis 

 Committee has investigated the electrical conductivity and the 

 freezing point of several dilute solutions of .salts, which furnish 

 some unexpected and, therefore, interesting results. The data 

 are, however, not yet complete. The report was accompanied 

 by a paper from Mr. Whetham on the measurement of the 

 electric conductivity, and one from Mr. E. H. Griffiths on the 

 freezing point determinations. Mr. S. Skinner has investigated 

 the carbon-consuming cell of Jacques, consisting of an iron 

 crucible into which is put fused caustic soda with a carbon 

 rod as electrode, the crucible forming the other electrode. 

 In order to maintain the electromotive force of the cell, air 

 is blown into the caustic soda. Mr. Skinner found that the 

 air acts by cleaning the surface of the iron crucible, and 

 can be usefully replaced by adding sodium peroxide to the 

 caustic soda. By measuring the current furnished by the cell, 

 and the loss of weight of the carbon electrode ])er second, the 

 author hopes to determine the electro-chemical equivalent of 

 carbon. Messrs. Cahen and Donaldson communicated the 

 results of some comparisons of the output and eflficiency of a 

 secondary cell (Tudor type) when charged at constant current 

 and constant electromotive force respectively. By charging at 

 constant potential the time of charging is reduced to le.ss than 

 half that required at constant current, the capacity is thirty per 

 cent, greater, but the energy efficiency is ten per cent. less. 

 Neither method of charging apjiears to damage the cell. Mrs. 

 Ayrton read a paper on the drop of potential at the terminals of 

 the electric arc, in which she described the exploration of 

 potential distribution in the arc by means of a third electrode of 

 carbon in.serted laterally. If the arc be maintained at constant 

 length the power expended at each carbon is a linear 

 function of the current, and if the current be maintained 

 constant the power expended at each carbon is a linear function 

 of the arc-length. The experiments are subject to errors 

 pointed out by Mrs. Ayrton in her paper: (i) the third 

 carbnn may not take up the potential of the point of the 

 arc in which it is placed ; (2) it alters the potential-distribu- 

 tion and the length of the arc. The author proposes to re- 

 peat her exj:)eriments, using an insulating third carbon. Prof. 

 Chattock described experiments to determine the velocity of 



NO. 1509, VOL. 58] 



electricity in the electric wind. He finds that the electricity in 

 the electric wind travels much more rapidly than the gaseous 

 particles themselves, reaching in hydrogen a velocity of 900 cm, 

 per second. Profs. Rosa and A. W. Smith have investigated 

 the healing effect of alternating currents upon the dielectric of a 

 condenser, measuring the net watts supplied to the condenser 

 and the heat developed per second in the dielectric. Their re- 

 sults were communicated to the Section by Prof. Rosa. Mr. F. 

 B. Fawcett described standard high resistances constructed by 

 depositing kathode films on ^lass and heating them for a long 

 time in a partial vacuum ; this process renders them constant. 

 Prof. Callendar exhibited a platinum voltmeter, in which the 

 change of temperature of a platinum wire on passing a current 

 through it is utilised to measure the current, and hence electro- 

 motive force ; the instrument is made self-recording. Mr. E. 

 H. Griffiths exhibited an apparatus for the measurement of re- 

 sistance, by which the resistance of a coil can be measured to 

 within one part in three millions. Prof. Lodge described a new 

 magnifying telephone, for calling up the operator at the receiving 

 end in .systems of wireless telegraphy. The minute current set 

 up in the receiving circuit passes through a small, light coil 

 suspended in a strong magnetic field and rigidly attached to 

 the disc of a microphone transmitter ; the coil moves, and so 

 sets the microphone disc in motion. A relay current in the 

 microphone circuit is thus interrupted, and can be sent through 

 the coil of a second similar apparatus. By using three or four 

 magnifications a slight sound can be made to approximate in 

 intensity to the human voice. Prof. Barrett, Messrs. \V. Brown 

 and R. A. Hadfield communicated the results of some deter- 

 minations of the electrical conductivity and magnetic perme- 

 ability of various nickel-steels. Prof. S. Lemstrom and Dr. E. 

 H. Cook read papers on the action of electricity on plants. Both 

 agree that the growth of plants is accelerated by electrical dis- 

 charges or currents ; Dr. Cook, however, considers that the 

 increased growth takes place only during germination of the 

 seed and its growth underground, the mature plant being un- 

 affected by electrical actions. In another paper Dr. Cook 

 described experiments on the reflexion of the brush discharge. 



The discussion on the magnetic and electrolytic actions of 

 electric railways was opened by Dr. Schott, who described the 

 total destruction of two American magnetic observatories by the 

 approach of electric street-railways. Prof. Riicker indicated 

 disturbances of a magnetometer needle due to the South London 

 Electric Railway felt as far away as 3^ miles, and referred to 

 the complete destruction of the Greenwich vertical force and 

 earth-current records. He pointed out that the trouble could 

 be remedied if electrical engineers would meet physicists in. 

 a friendly way, as they had done hitherto in this country. The 

 principal disturbances arise from want of in.sulation of the 

 return circuits of railway systems and the excessive distance 

 between the outward and return circuits ; the former gives rise 

 to earth-currents, and the latter 10 magnetic induction. Dr, 

 Eschenhagen stated that in conjunction with Prof, von Bezold 

 he had found a disturbance of magnetic instruments at a distance 

 of 15 kilometres from electrical railways near Potsdam. Mr. 

 W. H. Preece claimed protection for telegraphs and telephones 

 as well as for magnetic observatories ; the telephone, however, 

 when provided with a complete twisted metallic circuit, is not 

 capable of being disturbed, but earth-currents due to leakage 

 seriously interfere with telegraphic work. Signor Palazzo de- 

 scribed a method of damping the swings of a magnetometer 

 needle .so as to make it unsensitive to small-period oscillations. 

 Prof. Fleming gave many instances of corrosion of gas and 

 water pipes by electrolytic action, the pipes forming part of the 

 earth-return of a leaky circuit. Prof. S. 1*. Thompson suggested 

 the use of alternating currents and no earth-return, or of con- 

 tinuous currents with well-insulated circuits and the return wire 

 very close to the outward circuit. Prof. Ayrton pointed out 

 that it was to the advantage of the electrical engineer himself to 

 use a well-insulated return-circuit. 



In the di.scussion on the results of the recent solar eclipse 

 expeditions, Prof. Turner classified the work of solar eclipses as 

 referring chiefly to the shape, movements, nature and brightness 

 of the sun's surroundings. The success of Mrs. Maunder in 

 photographing a long coronal streamer has led to a discission 

 on the efficacy of triple-coated plates and a small camera, such 

 as she used. Again, evidence is very conflicting concerning the 

 relations of coronal extensions and solar prominences ; trom 

 their pasitions they appear to be connected, but spectro- 

 scopically there is no evidence of any such connection. Another 



