88 



NA TURE 



[March iS, 1909 



The transformations, which leave the electrodynamical 

 equations unaltered in form, are obtained by considering 

 the invariance of two integral forms of which the 

 coefficients are the components of the electric and magnetic 

 vectors. In obtaining those transformations use is made of 

 a pair of integral formulae which have been used as equiva- 

 lents of the electrodynamic equations by R. Hargreaves. 

 — The transformation of the electrodynamic equations of 

 moving bodies : E. Cunningham. The equations for 

 moving media have been deduced from the general electro- 

 dynamic equations by Lorentz by the use of a method of 

 averaging. The question discussed in the paper is that 

 of the changes produced in the equations for moving media 

 by those transformations for which the electrodynamic 

 equations are invariant. — The kinetic image of a convected 

 electric system formed in a conducting plane sheet : Prof. 

 J. Larmor. The question arises in connection with recent 

 observations of the magnetic fields in the neighbourhood 

 of sun-spots. It appears that such fields are confined to 

 thin layers, and this effect is traced to the action of con- 

 ducting layers in screening the magnetic fields due to 

 moving charges. The details of the screening action are 

 worked out by adapting the method used by Maxwell in 

 the discussion of the effects produced by a magnetic pole 

 moving in the neighbourhood of a conducting disc. — An 

 integral equation : G. H. Hardy. The paper is occupied 

 with functions defined by an integral formula which is a 

 generalisation of Fourier's integral theorem. — Term-by- 

 term integration of oscillating series : Dr. W. H. Youner. 

 — Further researches in the theory of elimination : A. L. 

 Dixon. 



Cambridge. 

 Philosophical Society. Februnrv 22. —Prof. Sedgwick, 

 president, in the chair. — The alleged influence of lecithin 

 on the determination of sex in rabbits : R. C. Punnett. 

 — Observations on the changes in the common shore crab 

 caused by Sacculina •. F. A. Potts. Giard first showed 

 that the association of the parasitic cirripedes, the Rhizo- 

 cephala, with crustacean hosts is the cause of sexual 

 modification in the latter. In the spider crabs, the male, 

 at the moult after infection, takes on all the external 

 characters which are associated with the female. These 

 changes are associated with the suppression of the gonads. 

 In the common shore crabs the modification is of a much 

 lower grade. In a single character the parasitised male 

 becomes intermediate between normal male and female. 

 The female, as in the case of the spider crabs, seems in- 

 capable of change toward the male type. The male 

 gonads may still remain in reproductive activity under the 

 influence of the parasite, though the female is restrained 

 from producing mature eggs. — .'\ so-called " sexual " 

 method of forming spores in bacteria : C. C. Dobeil. The 

 paper was an attempt to show that the process which 

 has been described as a " conjugation " in certain disporic 

 bacteria (Bacillus hiltschlii and B. flexilis) should really 

 be interpreted quite differently. From a study of the spore- 

 formation of Bacillns spirogyra and Bacterium lunula, 

 n.sp., the author was led to conclude that the " conjuga- 

 tion " represented really an abortive cell-division, and 

 hence that no " sexual " phenomena exist. The bearing 

 of these observations upon the problems of the sexuality 

 of the Protista and the affinities of the bacteria were briefly 

 indicated. — The migration of the thread-cells of Moerisia : 

 C. L. Bouieng^er. The thread-cells of the oral battery 

 of the Egyptian medusa M. lyonsi do not develop in situ, 

 but are formed in the more proximal parts of the manu- 

 brium, whence they make their way through endoderm 

 and structureless lamella to the ectoderm of the mouth 

 region. Similarly, the thread-cells on the tentacles develop 

 in the eye-bearing tentacle-bulbs and migrate to the 

 batteries when completely formed. — A note on a specimen 

 of Pelagothuria from the Seychelles : J. C. Simpson. 

 This pelagic holothurian was first discovered off the Pacific 

 coast of America by Agassiz in 18S0. Since then it has 

 been taken in the Indian Ocean by the Valdivia expedi- 

 tion, and in the North Atlantic by the Prince of IMonaco. 

 The present specimen was taken bv Mr. Stanley Gardiner 

 in 750 fathoms of water in the Indian Ocean north of the 

 Seychelles. The general features of its anatomy conform 



NO. 2055, VOL. 80] 



fairly closely to the published descriptions of previous speci- 

 mens, with the exception of the characteristic swimming 

 membrane, which in this case is composed almost entirely 

 of a sponge, which is evidently living commensally with 

 the holothurian. — The study of discontinuous phenomena : 

 N. R. Campbell. A further study of von Schweidler's 

 theory of radio-active " fluctuations," which has been 

 applied experimentally by Kohlrausch, Meyer and Regener, 

 and Geiger. The theory is put in a somewhat more 

 general and complete form, and its application to the inter- 

 pretation of observations with actual instruments con- 

 sidered at some length. Finally, the validity of the 

 experiments mentioned is discussed. 



Dublin. 

 Royal Irish Academy, Febtua'y 8. — Dr. F. A. 

 Tarleton, president, in the chair. — Theorems on the 

 twisted cubic ; M. J. Conran. It is shown that the three 

 diameters of a cubical hyperbola are situated in the " plane 

 of centres," and are the medians of the triangle formed 

 by the " points " of the curve in that plane. The inter- 

 section of the diameters is the centre of the " locus of 

 centres," and is also the centre of the hyperboidal locus of 

 poles of planes parallel to the plane of centres with respect 

 to the conic sections of the developable. It is, moreover, 

 proved that the osculating planes touch this hyperboloid, 

 and that the points of contact lie on a second twisted 

 cubic with the same plane of centres and the same three 

 diameters. A theory of correspondence is developed from 

 which a number of metrical theorems are deduced. Finally, 

 the geometrical interpretations of some of the invariant 

 and covariant forms of the general equation are given. — 

 Proofs of generalised Fourier sum theorems in trigono- 

 metrical and in Bessel functions : Prof. W. McF. Orr. 

 Proofs are given of expansions in some respects more 

 general than any which the writer has seen rigorously 

 treated. Any function, <l>(x), subject to Dirichlet's con- 

 ditions, is expressed between the limits a, b, in the form 



where the admissible values of A, B, and /i are deter- 

 mined by the equations 



AFjifi),-"" + BF„{f:L)e- f" = 0, AF3(MV''* + BFji»t-''J = o, 

 the F's denoting polynomials. A similar expansion in 

 Bessel functions is established which includes that 

 employed in the treatment of problems in vibratory motion 

 in the space between concentric cylinders and spheres. 

 The method is that of contour integration previously used 

 by Carslaw and others. The nature of the convergence 

 and the possibility of term by term differentiation is dis- 

 cussed to some extent. The statement in a previous paper 

 (see Nature, December 24, 1908, p. 240) of an integral 

 theorem analogous to Hankel's, involving the derivatives 

 of Bessel functions, is a blunder. — The limestone caves of 

 Marble Arch, Co. Fermanagh : H. Brodrick. Several 

 streams descending from the sandstone uplands sink when 

 they reach the limestone, reappearing at intervals at the 

 bottom of pot-holes or cliff-walled depressions, and return- 

 ing to the open after a distance of about a mile. The 

 course of the stream was determined, so far as practicable, 

 with the aid ol rope-ladder work in the pot-holes and a 

 good deal of wading and swimming in the caves. Com- 

 plete plans were submitted of the water-courses surveyed. 



Royal Dublin Society, February 23. — Prof. W. F. 

 Barrett, F.R.S., in the chair. — Mechanical stress and 

 magnetisation of iron : W. Brovwn. In this paper are 

 given some quantitative results obtained from experiments 

 with iron wires by varying the following four qualities : — 

 longitudinal magnetisation, longitudinal stress, circular 

 magnetisation, and the cross-sectional area of the wire. 

 The results so found are given in tables and curves. — The 

 quantity of the alkaloid taxine in yew: Richard J. Moss. 

 The leaves of common yew grown in south county Dublin 

 were found to contain 0-082 per cent, of taxine, calculated 

 from the weight of the leaves immediately after gathering. 

 The leaves of the varictv known as Irish vew or Florence- 



