282 



NATURE 



{Jan. 23, 1879 



SOCIETIES AND ACADEMIES 

 London 



Royal Society, January 9, — "On the Electromagnetic 

 Theory of the Reflection and Refraction of Light," by George 

 Francis Fitzgerald, M,A,, Fellow of Trinity College, Dublin. 

 Communicated by G. J. Stoney, M.A., F.R.S., Secretary of 

 the Queen's University, Ireland. 



. I have thrown the expressions for the electrostatic and electro- 

 kinetic energy of a medium given by Prof. J. Clerk-Maxwell in 

 his "Electricity and Magnetism," vol. ii. part iv. chap. 11., 

 into the same forms as 5l*Cullagh assumed to represent the 

 potential and kinetic energy of the ether, in " An Essay towards 

 a Dynamical Theory of Crystalline Reflection and Refraction," 

 published in vol. xxi. of the Transactions of the Royal Irish 

 Academy. Following a slightly different line from his, I obtain, 

 by a quaternion and accompanying Cartesian analysis, the same 

 results as to wave propagation, reflection, and refraction, as 

 those obtained by M'Cullagh, and which he developed into the 

 beautiful theorem of the polar plane. Of course, the resulting 

 laws of wave propagation agree with those obtained by Prof. 

 Maxwell from the same equations by a somewhat different 

 method. For isotropic media, the ordinary laws of reflection 

 and refraction are obtained, and the well-known expressions for 

 the amplitudes of the reflected and refracted rays. 



In the second part of the paper I consider the case of 

 reflection at the surface of a magnetised medium, adopting the 

 expressions Prof. J. Clerk Maxwell has assumed in "Electricity 

 and Magnetism," vol. ii. part iv. § 824, to express the kinetic 

 energy of such a medium. 



I show that the method adopted in my former paper on 

 Magnetic Reflection in the Proceedings of the Royal Society for 

 1876, No. 176, is justified, and that it is legitimate to consider 

 an incident plane polarised ray as composed of two oppositely 

 circularly polarised rays, each of which is reflected according to 

 its own laws. I consider next the cases of the magnetisation 

 being all normal to the surface, and all in the surface and the 

 plane of incidence, and obtain the following result : When the 

 incident ray is plane polarised, and the plane of polarisation is 

 either in or perpendicular to the plane of incidence, the effect of 

 magnetisation is to introduce a component into the reflected ray 

 perpendicular to the original plane of polarisation, which 

 vanishes at the grazing and normal incidences, and, in the case 

 of iron, attains a maximum at about the angle of incidence i = 

 63° 20'. 



I do not obtain any change of phase by reflection in any case ; 

 and this is to be expected, as this change of phase probably 

 depends on the nature of the change from one medium to 

 another, which, following M'Cullagh, I have uniformly assumed 

 to be abrupt. Apart from this question of change of phase, my 

 results conform completely to Mr. Kerr's beautiful experiments 

 on the reflection of light from the pole of a magnet, as published 

 in the Philosophical Magazines for May, 1877, ^^^ March, 1878. 



"On Dry Fog," by E. Frankland, D.C.L., F.R.S., Pro- 

 fessor of Chemistry in the Royal School of Mines. 



January 16. — " Concluding Observations on the Locomotor 

 System of Medusae," by George J. Romanes, M.A., F.L.S. 

 Communicated by Prof. Huxley, Sec. R.S. 



The principal bulk of the paper is devoted to a full consider- 

 ation of numerous facts and inferences relating to the phenomena 

 of what the author terms " artificial rhythm." Some of these facts 

 have already been published in abstract in the Proceedings of the 

 Royal Society" (vol. xxv.), and to explain those which have not , 

 been published would involve more space than it is here desir- j 

 able to allow. The tendency of the whole research on artificial j 

 rhythm, as produced in various species of Medusce, is to show 

 that the natural rhythm of these animals (and so probably of 

 ganglio-muscular tissues in general) is due, not exclusively to the 

 intermittent nature of the ganglionic discharge, but also in 

 large measure to an alternate process of exhaustion and restora- 

 tion of excitability on the part of the responding tissues— the 

 ganglionic period coinciding with that during which the process 

 of restoration lasts, and the ganglionic discharge being thus 

 always thrown in at the moment when the excitability of the 

 responding tissues is at its climax. 



Light has been found to stimulate the lithocysts of covered- 

 eyed Medusae into increased activity, thus proving that these 

 organs, like the marginal bodies of the naked-eyed Medusae, are 

 rudimentary organs of virion. 



The polypite cf Aiirelia aur'.la has been proved to execute 



movements of localisation of stimuli somewhat similar to those 

 which the author has already described a; being performed by 

 the polypite of Tiaropsis ir.dicans. 



Alternating the direction of the constant ciu-rent in the mui- 

 cular tissues of the Medusae has the effect of maintaining the 

 make and break stimulations at their maximum value ; but the 

 value of these stimulations rapidly declines if they are succes- 

 sively repeated with the current passing in the same direction. 



In the sub-umbrella of the Medusa: waves of nervous excita- 

 tion are sometimes able to pass when waves of muscular con- 

 traction have become blocked by the severity of overlapping 

 sections. 



Exhaustion of the sub-umbrella tissues — especially in narrow 

 connecting isthmuses of tissue — may have the effect of blocking 

 the passage of contractile waves. 



Lithocysts have been proved sometimes to exert their gai>- 

 glionic influence at comparatively great distances from their own 

 seats — contractile waves, originating at points in the sub-umbrella 

 tissue remote from a lithocyst, and ceasing to originate at that 

 point when the lithocyst is removed. A nervous connection of 

 this kind may be maintained between a lithocyst and the point 

 at which the waves of contraction originate even after severe 

 forms of section have been interposed between the lithocyst ami 

 that point. 



When the sub-umbrella tissue of Aurelia is cut throughout its 

 whole diameter, the incision will again heal up, sufficiently to 

 restore physiological continuity, in from four to eight hours. 



Chemical Society, January 16. — Dr. Gladstone, president, 

 in the chair. — The following papers were read : On the action 

 of isobutyric anhydride on the aromatic aldehydes, by W. H. 

 Perkin. The author has studied the action of isobutyric anhy- 

 dride on cuminic aldehyde, hydride of benzoyl, cinnamic aldehyde 

 paroxybenzoic and anisic aldehydes. The bodies formed are 

 respectively )3 isopropylbutenylbenzene, j8 butenylbenzene, butenyl- 

 cinnamene, parabutenylphenol, and ^ parabutenylanisoi'l. — On 

 two new methods for the estimation of minute quantities of 

 carbon and their application to water-analysis, by Drs. Duprc- 

 and Hake. The first consists in burning the substance in a 

 current of oxygen in a combustion tube with oxide of copper, 

 absorbing the carbonic acid in a Pettenkofer tube with baryta 

 water, filtering off the barium carbonate with great care, con- 

 verting it into chloride, then into sulphate, and weighing; in the 

 second, the carbonic acid passes into a 2 per cent, solution of 

 basic acetate of lead, and the turbidity compared with that pro- 

 duced by a solution of carbon of known strength in a Mills colori- 

 meter. — On stannic ethide, by Dr. Frankland and Mr. A. 

 Lawrance. By treating zinc ethyl with successive quantities of 

 fused stannous chloride, the authors have prepared stannic ethide 

 with great facility, they have also examined its properties, and 

 specially investigated the action of sulphurous acid. — Onaurin, 

 by R. S. Dale and C. Scliorlemmer. The authors have 

 prepared pure aurin with great care, and confirmed the formula 

 which they have already assigned to it. They have also studied 

 ammonia aurin, tetrabromaurin, and the compounds formed by 

 aurin with acetic, sulphuric, hydrochloric, and nitric acids. — On 

 the derivatives of diisobutyl, by W. Carleton Williams. — On 

 the action of chlorine upon iodine, by J, B. Hannay. ITie 

 author confirms his previous conclusion, viz., that a body con- 

 taining one atom of iodine and four atoms of chlorine does not 

 exist. 



Geological Society, January 8. — Henry Clifton Sorby, 

 F.R.S,, president, in the chair. — Charles Barrington Brown, 

 Carl Fischer, M.D., F.L.S,, William Coles Paget Medlycot, 

 were elected Fellows ; and Dr. F. V. Hayden, Washington, 

 and M. Jules Marcou, Salins, Foreign Members of the 

 Society. — The following communications were read : — On 

 some tin-deposits of the Malayan Peninsula, by Patrick 

 Doyle, C.E. (Communicated by the Rev. T. Wiltshire, 

 F.L.S.) The tin-ore of the Malayan Peninsula is obtained 

 from " stream-works " in an alluvial plain extending between 

 a range of granitic mountains and the sea. The author 

 describes the mines of the district of Larut Perak. The ore is 

 got in open workings at an average depth of about 10 feet. 

 The tin-bearing stratum has an average thickness of 4 '87 feet ; 

 it is overlain by stratified sand and clay, and rests upon either 

 porcelain clay or, sometimes, a sandstone. The ore varies from 

 a fine sand, near the sea, to a coarse gravel, near the mountains, 

 and is mixed with quartz, felspar, mica, and schorl. The author 

 is of opinion that the strctiim of ore has been derived from the 

 OTanite of the mountain raige, in which it itiU occurs in veinf. 



