April 12, 1906] 



NA TURE 



575 



land-ice — which, as it involves some serious difficulties, 

 cannot yet be taken for granted. That ice is capable of 

 shearing off and thrusting before it large masses of rock 

 is also an hypothesis, fcr which the author, after doing his 

 best to study ice-work in the field, can find no valid evidence, 

 lie maintains that these sections do not suggest the above 

 explanation-. At the Pinner's Cross Pit the Boulder-clay is 

 not, strictly speaking, " banked-up " against the Chalk, 

 but occupies a hollow in the Chalk. In the pit south-west 

 of Newsell's Park, a shear-plane can indeed be seen in 

 one face, which, however, is explicable by ordinary fault- 

 ing. A few yards farther to the south-east, Boulder-clay 

 appears above the floor of the pit, filling an arched cavity. 

 This is, no doubt, a singular position, but there is nothing 

 to show that the Chalk has been thrust over the Clay. 

 The author suggests that, as in Moen, the Clay has been 

 carried down from above into cavities already formed in the 

 Chalk. — Brachiopod homceomorphy : Pygope, Antinomia, 

 Pygites : S. S. Buckman. This paper deals with the 

 diphyoid Terebratula;, of which so many species have borne 

 the name Terebratula diphya (Colonna). It is pointed out 

 that this name is pre-Linnean, and can only date from the 

 time when it was revived by L. von Buch in 1834. It 

 appears that Terebratula diphya is not the type of the 

 genus Pygope. Reasons are given for taking as the type 

 of Pygope one of the forms of T. antinomia which is 

 considered to be the same species as T. deltoidea, Val. 

 Then the later generic name Antinomia, Catullo, is dis- 

 cussed. The genus was founded on five species, and one 

 of them is now selected as the type — the genolectotype. 

 This is A. dilatata, Catullo, supposed to be equivalent to 

 Terebratula antinomia, Catullo, that is, to what is now 

 selected to be the type of that species. In that case the 

 species would bear the name Antinomia antinomia (Cat.). 

 But there is yet another series of diphyoids, typified by 

 Terebratula diphyoides, d'Orb. It is pointed out that, 

 although the species covered by the name diphyoides are 

 very like Pygope as now used, yet they all differ in having 

 particular characters in the preperforate stage — a dorsal 

 ridge and a ventral sulcus. 



Koyal Microscopical Society, March 21. — Rt. Hon. 

 Sir Ford North, P.C., F.R.S., vice-president, in the chair. 

 — A contribution to our knowledge of the Rotifera of 

 South Africa : C. F. Rousselet. — A new form of finder 

 which can be used on any microscope, and by which the 

 object registered on one microscope can be found on any 

 other : J. M. Coon. — Some Oribatida; from Sikkim : 

 N. D. F. Pearce. Most of the tropical species were on 

 the average smaller than those found in temperate climes. 

 — The limits of resolving power for the microscope and 

 telescope : E. M. Nelson. 



Entomological Society, March 21. — Mr. F. Mfrrifielrl, 

 president, in the chair. — Six rj ,j examples of the 

 Pifrine genus Eronia with corresponding 9 9s: Dr. 

 F. A. Dixey. Attention was directed to the extreme 

 diversity shown by the $ $ s in these closely allied 

 species. Dr. Dixey considered that this characteristic 

 was due to the fact that in every instance the had been 

 diverted from the ordinary aspect of the group by the oper- 

 ation of mimicry, either Miillerian or Batesian. The 

 species of entirelv different affinities which had acted pre- 

 sumably as models were associated also with the exhibit. 

 — Two specimens of Emmelcsia unifasciata which emerged 

 in August last from pupae which had lain over since the 

 autumn of 1900, thus having passed five seasons in the 

 pupal stage : R. Adkin. — Progressive melanism in the 

 Riviera of Hastula hyerana : Dr. T. A. Chapman. ,\ 

 discussion followed on melanism and its causes. 



Physical So e v. March 23.— P10'. J. Peiry, F.R.S., 

 president, in the chair. — Unilateral electric conductivity 

 over damp surfaces : Prof. F. T. Trouton. Some time 

 ago the author noticed a rather perplexing difference in 

 electrical resistance depending on the direction in which 

 the measuring current was passed. The resistance under 

 examination was that of the layer of moisture which 

 adheres to glass when exposed to moist atmospheric con- 

 ditions. The arrangement in which this resistance 

 measurement was effected was one used for determining 

 the temperature of deposition of dew. For this purpose 

 two parallel wires of platinum were melted on to a glass 



NO. I902, VfL. 73] 



surface at a small distance apart. The surface could be 

 artificially cooled. A cell and a galvanometer were inserted 

 in series with the two platinum wires. As soon as moisture 

 condensed on the glass the circuit was completed and a 

 current passed, thus permitting the accurate determination 

 of the dew-point. When a delicate galvanometer is used 

 a small current can be detected long before the true dew- 

 point is reached. It is at this stage that the anomalous 

 behaviour in the resistance is found. On passing a current 

 across the glass surface when exposed to ordinary atmo- 

 spheric conditions, it was found to diminish to a certain 

 minimum value, the amount of which depended on the 

 hygrometric state. On reversal, the current assumed its 

 original value, and then diminished to a minimum as 

 before, and so on for further reversals. In order more 

 conveniently to study the matter with larger currents, tin- 

 foil grids were prepared by pasting strips of tinfoil on to 

 glass plates. The theory put forward to account for the 

 phenomenon depended on the transportation of moisture 

 over the surface by the current. In this way the effective 

 thickness of the layer might be much diminished by a 

 banking up of the moisture along the edge of one of the 

 metallic electrodes. — The construction and use of oscillation 

 valves for rectifying high-frequency electric currents : Prof. 

 J. A. Fleming-. The author recalled the fact that so far 

 back as 1890, when investigating the Edison effect in glow- 

 lamps, he had shown that the space between the incan- 

 descent carbon filament and an insulated metal plate placed 

 in the vacuous bulb possessed a unilateral conductivity, 

 negative electricity being able to pass from the filament 

 to the plate, but not in the opposite direction. This led 

 him to suggest an arrangement of the above kind for 

 separating out or rectifying the oppositely directed currents 

 in an alternating current. This effect was now recognised 

 as due to the copious emission of negative ions or electrons 

 from the incandescent carbon. It was by no means 

 obvious, however, before trial, that any such rectifying 

 arrangement or valve would operate with currents of very 

 high frequency. For example, electrolytic rectifiers such 

 as the aluminium-carbon cell were not available for high- 

 frequency currents because a time element entered into the 

 chemical actions involved. In 1904, however, the author 

 discovered that if the carbon filament in an electric glow- 

 lamp was surrounded with a metal cylinder connected to 

 an insulated terminal by a wire sealed through the bulb, 

 and if the filament was made incandescent by an insulated 

 battery, then between the insulated terminal and the 

 negative pole of the battery a unilateral conductivity existed 

 which was operative with currents of any frequemv. and 

 the valve so made might be employed to render electrical 

 oscillations measurable by an ordinary sensitive galvano- 

 meter. The author exhibited oscillation valves made on 

 this plan. — The use of the cymometer for the de- 

 termination of resonance curves : G. B. Dyke. The ex- 

 periments described in the paper were made with a view 

 to the adaptation of the direct-reading cymometer to the 

 delineation of resonance curves and the determination of 

 the logarithmic decrements of wave trains and the resist- 

 ance of oscillating sparks. 



Edinburgh. 

 Royal Society, February 19. — Dr R. If. Traquair, vice- 

 president, in the chair. — The elevation of the boiling point 

 of aqueous solutions of electrolytes : Rev. S. M. 

 Johnston. The paper contained a detailed account of 

 the method of experiment, and after giving the experi- 

 mental results in a number of cases, proceeded to examine 

 into reasons for the observed increment in the value of 

 the elevation constant as indicated by theory. When the 

 ratio of the molecular conductivity for a given concentra- 

 tion to the value for infinite dilution was plotted against 

 the elevation constant, the graph for each salt was, up to 

 a certain ionisation, a straight line parallel to the ionisa- 

 tion axis, but changed direction at this point. Arguments 

 were adduced that this increment in the value of the 

 elevation constant was due to hydration ; and if this ex- 

 planation be assumed, the observations gave a means of 

 determining the ionisation, and therefore the concentration, 

 at which hydration commences. Thus for solutions of 

 Cdl,, Li CI, N'H.Br, and NH,I, with concentrations respec- 

 tively of 18, 092, 0-74, and 07 gram equivalents per litre, 



