September 28, 1893 J 



NATURE 



527 



during the last thirty years of sun-spots, iS;c., and stated that he 

 had not on a single occasion been able to verify the assertions 

 made in 1769 by Dr. Wilson with reference to the behaviour 

 (through fore-shortening) of the umbra and penumbra as a i-un- 

 spot approaches the limb of the sun. 



On Friday a report was submitted "On our Present Know- 

 ledge of Electrolysis and Electro-Chemistry." This was part 

 of a report which was being drawn up by Mr. W. N. Shaw 

 and Mr. T. C. Filzpatrick. Many investigators have been 

 engaged upon electrolytic work, but their observations have 

 been puVilished in scattered papers and expressed in a manner 

 which makes comparison of them difficult. The present in- 

 stalment of the report is the work of Mr. Filzpatrick, who has 

 at great pains collected all the available information on the 

 electro-chemical properties of solutions in water and has com- 

 piled an exhaustive table .'•howing the different chemical salts 

 in solution. Data are given respecting conductivity, tempera- 

 ture coefficients, migration constants of ions (from which one 

 can calculate the rate at which ions travel through solutions), 

 fluidity (the inverse of viscosity), &c. As with falling olijects 

 so it is with ions ; they travel more quickly through a limpid 

 fluid than through a viscous one. This is just why acids con- 

 duct belter than salts. 



On the lOntiectii'U het-vccn tlie Etiier and Mailer : — Prof. O. 

 Lodge made a fuither repoit as to experiments made with the 

 same apparatus as that which he had described to the Section 

 at the Cardiff meeting in 1S91. Ever since Fresnel's time the 

 question has been debated whether — (i) the earth carries with 

 it the ether in its immediate neighbourhood, thus causing a dis- 

 turbance, or (2) rushes through it, and it through the earth, each 

 being independent and moving independently. Dr. Lodge has 

 been endeavouring to settle this question byfinding out whether a 

 rapidly revolving steel disc (like a circular saw) exercises any drag 

 upon the ether in its immediate neighbourhood. He uses two 

 such discs of tough steel, about a yard in diameter, rotating in 

 parallel planes an inch apart. He is now able to run the discs 

 at the rate of 3000 revolutions per minute ; but even at this 

 high speed no effect is observed which can be attributed to any 

 drag of the ether. He has also replaced the discs by an oblate 

 spheroid of wrought iron with a deep channel or groove cut 

 in it and wound with wire ; but the rotation of this transversely 

 magnetised mass (weighing about a ton) does not set the ether 

 in motion. 



A Mechanical Analogue of Anomalous Dispersion. — Mr. Glaze- 

 brook described a mechanical model which he had constructed 

 to illustrate the theory of anomalous dispersion propounded by 

 Sellmeyer, and developed by Helmholtz and Lord Kelvin. 

 The model consisted of rows of balls connected to each other 

 by elastic strings and connected to fixed beams by springs of 

 varying stiffness. 



Prof. Fitzgerald communicated a note on Prof. Eberl's method 

 of estimating the radiating power of an atom, and stated that 

 the results show that molecules have a complex structure, other- 

 wise iheywould radiate very badly. Prof. Fitzgerald holds 

 that the vibration of an atom is the mechanical vibration of a 

 minute bit of the corresponding mailer; and that the ionic 

 charges by their corresponding vibrations excite the external 

 radiation. 



Lord Rayleigh gave the results of his investigations on the 

 "Theory of Reflection from Corrugated Surfaces," and also, in 

 the absence of the author (Lord Kelvin), read two papers 

 " On the Piezo-Eleciric Property of Quartz," and •' On a Piezo- 

 Electric Pile." These were followed by two interesting com- 

 munications on electromagnetic work carried out under the 

 iirection of Prof. Hertz in Bonn. 



On Electric Interference Phenomena.— 'Mr. E. H. Barton 

 described experiments on phenomena somewhat similar lo 

 Newton's rings, but exhibited by electromagnetic waves in 

 wires. The waves were generated by a Hertzian primary 

 oscdlator consisting of two discs of 40cni. diam. each connected 

 by a wire im. long to small brass balls between- which sparks 

 passed. Opposite these discs, and about 30cm. distant, were two 

 similar ones from which proceeded a pair of parallel copper wires 

 8 cm. apart and 160 m. long. Along these the waves were propa- 

 gated and the interference phenomena exhibited. The phenomena 

 in question were produced by hanging sheets of tinfoil on the 

 wires for a certain part of iheir length. Where the sheets 

 hung the capacity and self-induction 01 the leads were changed, 

 thus causing a partial reflection of the waves from the begin- 

 iiingof this abnormal part. But a second reflection occuis at 



NO. 1248, VOL. 48] 



Mie ena of this part also. Thus interference phenomena were 

 ^et up, and as the length of the abnormal part was gradually 

 increased the intensity of the transmitted waves was found to 

 periodically increase and diminish. Mr. Barton has recently 

 given (Proc. Koy. Soc.) a theory of these phenomena with 

 which the experiments are in fairly good accord. 



On the I'assage of Electric Wa-,ies tlirough Layers of Elec- 

 trolyte. — The method and apparatus used in this research were 

 descril^ed by Mr. G. 11. Yule in a communication to the Royal 

 Society in June last, and an experimental curve was given in 

 the same paper showing that the transmission of trains of elec- 

 tromagnetic waves through a layer of distilled water follows the 

 same law as that of light through a thin plaie, i.e. that the 

 transmitted intensity varies periodically as the thickness of the 

 plate increases. Similar curves were now given, using dilute 

 bohuions of zinc sulphate, alcohol, and a mixture of alcohol 

 and water ; in all cases the periodic character of the curve was 

 very well marked. As the transmitted intensity attains its first 

 maximum when the thickness of the layer is half a wave-length, 

 the nietnou may be used to deteriiiiiie dielectric constants. 

 That found for water was 69'5, and for 95 percent, alcohol 

 267— values agreeing roughly with the high values found by 

 previous investigators. 



Mr. J. Larmor referred to a familiar type of caustic curve, 

 produced by reflection from a strip of metal bent into circular 

 form. He pointed out that the source of light need not lie in 

 the plane on which the caustic is thrown — the caustic preserves 

 the same form whether the incidence i^i direct or indirect. 



On Saturday the following papers (mainly of mathematical 

 interest) were communicated : — " On a Spherical Vortex," by 

 Prof. M. J. M. Hill; "Note on the Magnetic Shielding of 

 Two Concentric Spherical Shells," by Prof. RUcker ; "The 

 Eff'ect of a Long Tube as a Magnetic Screen," and "The Effect 

 of a Hertzian Oscillation on Points in its Neighbourhood," by 

 Prof. Fitzgerald ; "The Magnetic Action of Light,", by Mr. J. 

 Larmor (Dr. Lodge characterised this as being perhaps the 

 most suggestive communication made during Ihe meeting, and 

 expressed the hope that it would be further developed and 

 printed) ; "A Special Class of Generating Functions in the 

 Theory of Numbers," by Major MacMahon ; "On Agreeable 

 Numbers," by Lieut.-Col. Cunningham. 



On Monday Mr. Plorace Darwin exhibited and described the 

 instruments used by the Committee on Earth Tremors. Prof. 

 Milne presented the report of the Committee on the volcanic 

 and seismological phenomena of Japan, and gave a most in- 

 teresting ^account of the work done by himself and other 

 observers in Japaif. 



The greater part of the sitting was taken up by a discussion 

 on the teaching of elementary physics. This was introduced 

 by Prof. Carey Foster, who exhibited and described some 

 simple and cheap apparatus for teaching practical physics. The 

 apparatus shown was well adapted for elemc'itary class-work in 

 heat and electricity. Mr. W. B. Croft followed with a paper 

 in which he described the plan of science teaching at Win- 

 chester School, where, by an order of the Privy C<nincil, science 

 is compulsory for almost nil the lioys. The aim is to arrange 

 for that which may be imposed on all .as jjart of a good educa- 

 tion — to supplement thought with the observing faculty. The 

 scheme is also suited for those who may hope to become 

 mathematical physicists and who should in boyhood devote 

 themselves mainly to mathematics. For some boys science 

 forms the best foundation of early education. I'ublic schools 

 are not generally adapte.l fur these cases ; but they can well be 

 provided for by a lib.-ral elasticity of system. Prof. O. Lodge 

 read a paper in which Mr. A. E. Hawkins gave the results 

 of his experience of science teaching in public schools, 

 especially in Bedford School. He deprecated the influ- 

 ence of examinations on the teacher's work. Dr. 

 Gladstone considered that apparatus should be not only 

 cheap but simple. To use complicated apparatus was almost 

 as dangerous as to depend upon blackboard wot k. He agreed 

 with Mr. Buckma^ter that too much work was usually expected 

 from a science master. Mr. I). E. Jones emphasised the last 

 point, and stated that instances ha \ come under his notice 

 where science masters had no time to prepare their experiments 

 for class. The idea that science, unlike other subjects, ought 

 to pay lor itself, was much to be deprecated ; it should not^be 

 neglected or abandoned ill a school merely because it was costly. 

 The teaching of physics as an educational instrument had not 

 been sufficiently developed ; and Continental schools were not 



