OcTOIiEK 8, 1S96J 



NA TURE 



567 



this confi^urution and of the modification which it experiences 

 in the formation of ice-crystals were shown ; also of right- and 

 left-handed ciuartz molecules and rock-crystal. The crystalline 

 molecule of quartz is supposed to consist of three of the chemical 

 molecules (OSiO). >lr E. Rutherford exhibited, by a number 

 of interesting experiments, a method of detecting electromag- 

 netic waves. The detector consists of a group of fine steel wires 

 about I cm. long, insulated from each other by shellac. These 

 are first magnetised, and then inserted in a coil of many turns 

 of wire provided with a suspended magnet and mirror. The 

 passage of Hertzian waves alters the magnetism of the group of 

 magnets, and shifts the position of tlie spot of light. For long 

 waves the detector is very sensitive, and has been found to 

 respond to waves produced half a mile away \vi\Cn houses 

 betiveen) ; but for short waves a coherer is much more sensitive. 

 The method has been used for niea.suring the resistance of a 

 spark-gap: for .short sparks this is very slight, but increases 

 much more rapidly than the length of the gap. The apparent 

 resistance of iron wires to Hertzian wave-, is found to be from 

 10 to 100 times that for steady currents. J'rof. J. Chunder Bose 

 exhibited a very neat and compact apparatus forslud)ing the 

 properties of electric waves. With this lie has verified the laws 

 of reflection and refraction, determined refractive indices and 

 wave-lengths (by curved gratings), and exhibited polarisation 

 ind double refraction by pressure and unequal heating. The 

 gratings used consist of tinfoil strips on ebonite. Between 

 crossed gratings tourmaline exhibits little or no depolarising 

 effect ; the difference of transparency for the two vibrations at 

 right angles is nothing like what it is for light. \ery good 

 depolarisalion is produced by beryl and by serpentine ; the 

 (alter makes a good electrical tourmaline. So also does a block 

 of jute compressed by hydraulic pressure. Vegetable fibres and 

 locks of human hair produce very striking polarisation effects, 

 the vibrations along the fibres being absorbed, and those at right 

 ingles transmitted. 



Department II. met in th? Physics class-room to consider 

 re ports and papers on Meteorology. Reports of four Committees 

 were submitted : on Meteorol igical Observatio:is on Ben Nevis ; 

 on Solar Radiation ; on Seismological Observations ; and on 

 Meteorological Photographs. Mr. A. W. Clayden's report on 

 the application of photography to the elucidation of meteoro- 

 logical phenomena stated that the work of the Committee during 

 the past year had been almost entirely confined to the deter- 

 mination of cloud altitudes by the photographic method. The 

 l«o observing cameras are stationed 200 yarns apart, and are 

 electrically connected by telegraph wires. Exposures of quarter 

 of a .second and less are used. Each negative contains an image 

 <if the sun. The altitude and azimuth of this are first deter- 

 mined, and the coordinates of a selected point in the cloud- 

 image are measured with reference to this, .\mong the greatest 

 altitudes measured are the following (in miles) :— Mackerel sky, 

 725; cirro-stratus, 9'63 ; cirrus, 1 1 '62 ; upper level cirrus, 

 I7'02. The results show that clouds forming exhibit a general 

 tendency to rise, and this is also true of the ascent of general 

 cloud-levels towards the early afternoon. Papers were read by 

 I'rof. Kambaut, on the effect of refraction on the diurnal niove- 

 nienl of .stars, and a method of allowing for it in astronomical 

 photography; by Mr. ('<. 11, Bryan, on the sailing flight of 

 jjirds ; by the Rev. R. Harley, on the Stanhope arithnietic.il 

 machine of 1780 ; and by Mr. .\.. L. Rotch, on the exploration 

 of the upper air by means of kites. 



In the adjourned discussion on Prof. Hose's paper, on Tuesday, 

 I'rof. Oliver Lodge exhibited the coheter. " copper hat," &c., 

 which he had used in studying electric wavis some three years 

 ago. He characterised his apparatus as being rather un 

 manageable and very cumbersome as compared with that of 

 I'rof. Bose: but members who were present at the Oxford 

 meeting will remember with gratitude Prof. Lodge's interesting 

 address, and the very successful experiments with which it was 

 illustrated. Mr. W. II. Preece m;ule a brief statement as to 

 telegraphy liy Hertzian vibrations. Signals have been trans- 

 mitted (by Signer Marconi, working with Mr. Kempe) across a 

 distance of one and a quarter miles on Salisbury PUain ; further 

 exoeriments are to be made on the Welsh hills. Reports were 

 submitted by the Committee on Electrolysis and the Electrical 

 Standards Committee. At the Ipswich meeting (see Nature, 

 September 26, 1895) the choice of ^ thermal unit was referred to 

 this Committee, which has since communicated with physicists in 

 various foreign countries on the matter. For many purposes 

 heat is most conveniently measured in ergs. The name Joule 



NO. 1406, \0L. 54] 



has been given to 10" ergs. A certain nuaiber of Joules may be 

 selected as a secondary or practical thermal unit, and called a 

 Calorie. According to the best determinations made, 4"2 Joules 

 are required to raise the temperature of i gm. of water from 

 9' '5 C. to lO^'S C. , measured by a hydrogen thermometer. The 

 Committee recommend that this be adopted as the secondary 

 thermal unit. More accurate determinations of J, and of the 

 variations of the specific heat of water, may neces-sitate a slight 

 alteration in the mean temperature at which the rise of 1° takes 

 place ; but the definitions and the number (4'2) of Joules in a 

 Calorie would otherwise remain unaltered. It is now proposed 

 to issue a circular requesting international co-operation and agree- 

 ment. Mr. W. N. Shaw read a paper on the total heat of water. 

 Rowland's measurements give us data for finding the specific 

 heat of water from o' to 35° ; and his measurements, together 

 with those of Regnault, enable us to calculate it from 100° to 

 180°. What is now needed is a series of determinations from 

 35^ to 100°. Ml. E. H. Griffiths exhibited a special form of 

 resistance box (which admits of easy recalibration of all the coils 

 in the box without requiring any other special instruments), and 

 briefly communicated the results of his measurements of electrical 

 resistance. It is of extreme importance that no shoulders should 

 form on the brass plugs. Standard coils of the B..A. pattern 

 (with wires imbedded in paraflin) only acquire the temperature 

 of the surrounding medium very slowly ; it is impossible to make 

 accurate determinations with them when the temperature of the 

 room differs from that of the bath by more than the fraction of a 

 degree. In Mr. Griffiths' box all the coils are of n.iked wire 

 wound on mica, and immersed in a hydrocarbon oil which is 

 stirred from the outside. Mr. S. A. Sworn communicated the 

 results of long and careful researches on absolute mercurial 

 thermometry, and emphasised the importance of capillary 

 corrections. 



On Wednesday the Section again divided into two depart- 

 ments. In the Physics class-room the Report of the Committee 

 on the sizes of pages of periodicals was presented, and papers 

 were read by Mr. W. H. Preece, on disturbance in submarine 

 cables ; by Mr. W. M. Mordey, on carbon megohms for high 

 voltages, and on an instrument for measuring magnetic perme- 

 ability ; by Mr. A. P. Trotter, on a direct-reading form of 

 Wheatstone Bridge ; and by Prof. F. Bedell, on the division of 

 an alternating current in parallel circuits with mutual induction. 



In the Physics Theatre Prof. J. E. Keeler described his method 

 of measurements of the velocity of rotation of the planets by the 

 spectroscopic method. Profs. Elster and Geitel described their 

 investigations as to the cause of the surface colourisation of colour- 

 less salts (KCl,NaCl) by the k.athode rays discovered by Goldstein. 

 In this process the in.side of the exhausted tube becomes coated 

 with a layer which looks as if it might be metallic potassium or 

 sodium. If so, it should be incapable of retaining a negative charge 

 under the influence of violet light ; this was tried, and found to be 

 Ihecase. In the case of rubidium and ciesiuni, gas-light was enough 

 to cause leakage. But Goldstein finds that the salts retain their 

 .superficial tints in air for months ; so the effect can scarcely be 

 due to free alkali-metals on the surface. Probably the molecules 

 of the metal are driven by the kathode rays into the salt, form- 

 ing a solid solution in van 't Hoffs sense. It has been shown 

 that the silts become alkaline after kathodic radiation, and this 

 indicates that chlorine has been driven off. No chemical lest 

 has shown the presence of Iree chlorine ; but this is not surprising 

 when we consider the difliculty of proving its presence after 

 light has acted upon silver chloride. A paper by Mr. J. Burke, 

 on change of absorption accompanying fluorescence, dealt with 

 a number of experiments made with the view of detecting 

 whether the coefficients of absorption of uranium glass, and some 

 other substances for the rays they emit, are altered in the act of 

 fluorescence. The experiments, which were described at length, 

 showed that a marked difference existed in the two cases, the 

 absorption being greater when fluorescing and when not. 

 Comparisons were made photographically as well as photo- 

 metrically. Mr. W. Barlow read a paper on homogeneous 

 structures and the .symmetrical partitioning of them, with 

 application to crystals. 



The interest of the sectional meetings was much enhanced by 

 the discussions following the papers, in which the President, 

 Lord Kelvin, Sir George Stokes, and Prof. G. F. Fitzgerald fre- 

 quently took part. So also did Prof. Oliver Lodge, who placed 

 at the disposal of the Section all the conveniences of his lecture- 

 rooms and laboratories, and also attended to the comfort and 

 convenience of members in other ways. 



