/4 



NATURE 



[March 20, 19 13 



belt of the syncline, and inclined outwards on either 

 side. 



Physical Society, February 28.— Prof. A. Schuster, 

 F.R.S., president, in the chair. — Prof. C. G. Barkla 

 and G. H. Martyn : The authors have made a pre- 

 liminary investigation of the Rontgen radiation pro- 

 ceeding- from a crystal of rock salt (which is of the 

 simple cubical form) when a pencil of Rontgen radia- 

 tion is incident in a direction nearly grazing one of 

 the three sets of mutually perpendicular cleavage 

 planes. Reflection of X-rays by the cleavage planes. 

 — Using a very narrow pencil of radiation, it was seen 

 that the principal secondary pencil was one obeying 

 the laws of reflections from the cleavage planes. A 

 pencil diverging in all directions from a point source 

 produced a corresponding reflected pencil of radiation 

 converging to a line focus after reflection from a set 

 of parallel cleavage planes. The quality of the radia- 

 tion forming the secondary pencils was shown both by 

 the photographic and by the ionisation method to be, 

 not the fluorescent X-radiation, but of the kind pre- 

 viously_ described as scattered X-radiation. It was 

 approximately of the same penetrating power as the 

 primary radiation, and was approximately homo- 

 geneous, having traversed 5 mm. of rock salt in the 

 case investigated. Interference fringe systems. — A 

 diverging pencil of radiation was directed on to a 

 crystal so that various portions were incident on the 

 cleavage planes at different angles. A photographic 

 plate showed the relative intensity of the correspond- 

 ing reflected radiations. It was seen that the intensity 

 of the reflected pencil varied periodically with varying 

 angle of incidence, the maximum being separated by 

 intervals corresponding to approximately equal incre- 

 ments in the value of cos 6, where 8 was the angle 

 of incidence on the reflecting planes. Such a series 

 of maxima may be explained by interference of the 

 pencils reflected from equal spaced parallel planes, 

 the maxima being spectra of various orders. The 

 wave-length, calculated on the assumption that these 

 are planes passing through corresponding portions of 

 molecules in the planes of cleavage, and that a mole- 

 cule is simply NaCl, is found to be o-6 x 10- 9 cm. If 

 the molecule be more complex, the calculated wave- 

 length would be greater. This value thus agrees 

 remarkably well with the value (between 1 and 

 2xio- 9 cm.) calculated from the velocity of ejection 

 of electrons by this X-radiation, taking this to behave 

 as ultra-violet lig-ht of short wave-length. There can 

 be little doubt that the fringe systems are interference 

 fringe systems. That the smaller system is a series 

 of spectra of different orders and the other an inter- 

 ference band system seems probable ; this theory cer- 

 tainly explains the results observed up to the time of 

 writing. — Prof. E. Wilson : Alternating-current mag- 

 nets. It follows from the well-known' law of pull of 

 an electromagnet that if the magnetic field alternates 

 between positive and negative values the pull is un- 

 directional and intermittent. Unless means are pro- 

 vided to reduce the consequent chattering and vibra- 

 tion, the maernet is rendered useless. In the present 

 experiments a phase-splitting device has been adopted, 

 and consists in surrounding a portion of the pole- 

 piece of the magnet with a short-circuited coil. The 

 portion of the pole-piece so surrounded is sometimes 

 said to be " shaded," and the coil referred to as a 

 "shading" coil. The effect of this coil is to alter, 

 not only the relative amplitudes, but the phase of the 

 magnetic fields passing through the shaded and un- 

 shaded portions of the pole-face. 



Linnean Society, March 6.— Prof. E. B. Poulton, 

 F.R.S., president, in the chair. — Geoffrey Smith : The 

 development and inheritance of sexual characters. 

 ''Discussion.') 



NO. 2264, VOL. 91] 



Zoological Society, March 4.— Dr. A. Smith Wood- 

 ward, F.R.S., vice-president, in the chair. — Dr. F. E. 

 Beddard : The anatomy and systematic arrangement of 

 the Cestoidea. A new genus of tapeworms, of the 

 family Ichthyotasniidae, from the crossed viper 

 (Lachesis altemans) was described. — Dr. W. A. 

 Cunnington : The Branchiura collected by the third 

 Tanganyika expedition in 1904-5. The collection con- 

 tained more than 300 specimens, and proved that in 

 the case of this group of animals also. Lake Tangan- 

 yika exhibits a number of endemic forms. While two 

 species of Argulidae are known to be widely distri- 

 buted in the lakes of Africa, they are associated in 

 Nyasa with a single form peculiar to that lake, but 

 in Tanganyika with no less than seven new types. 

 Tanganyika is thus shown to possess not only a con- 

 siderable number of characteristic species, but a much 

 richer Branchiuran fauna than the other great African 

 lakes. The paper was illustrated by lantern-slides 

 made from photomicrographs of the new species.- — W. 

 Schaus : Descriptions of a large number of new' species 

 of Rhopalocera from Costa Rica. More than 100 

 species had been collected, and of these fifty-four were 

 found to be new. — Dr. A. Willey : Notes on plankton 

 collected across the mouth of the St. Croix River, Xew 

 Brunswick, in July and August, 1912. 



Mineralogical Society, March 11.— Prof. H. L. Bow- 

 man, vice-president, in the chair. — W. Campbell 

 Smith : The mineral collection of Thomas Pennant 

 (1726-98). The collection, which has recently been 

 presented to the British Museum by the Earl of Den- 

 bigh, is accompanied by three volumes of manuscript 

 catalogue written in 1757. The classification used in 

 them is based, with some modifications, on Wood- 

 ward's "Natural History of the Fossils of England," 

 published in 1729. Special mention is made of 

 specimens presented by Borlase, Pontoppictan, and da 

 Costa, and the minerals from Flintshire were treated 

 in some detail. Several specimens were described by 

 Pennant in "A Tour in Wales." — Arthur Russell : The 

 minerals and mineral localities of Montgomeryshire. 

 Of the species described the more remarkable are 

 aurichalcite, from Llanymynech Hill Mine, Llan- 

 ymyneeh ; harmotome in double twins, associated with 

 barytes and witherite, from Cwm-orog Mine, Llan- 

 gynog; hydrozincite, which forms a remarkable 

 recent deposit on the sides of a level in the Van Mine, 

 Llanidloes ; pyromorphite from Aberdeunant Mine, 

 Llanidloes, and Llanerch-yr-aur Mine, Llanbrvnmair ; 

 witherite, from Cwm-orog Mine, Llangynog, Gorn 

 Mine, Pen-y-gaer Mine, and Pen-y-clyn Mine, Llan- 

 idloes, the crystals from the last being noteworthy on 

 account of the almost entire suppression of the alter- 

 nate faces of the pseudo-hexagonal prisms and 

 pyramids. — Dr. G. F. Herbert Smith : A new stereo- 

 graphic protractor. The novelty consists of a curved 

 ruler, made up of a combination of springs, which 

 sensibly retains a circular curvature within the limits 

 for which it is required. At the centre of the arc it 

 is clamped to an arm, movable in a groove and carry- 

 ing a scale, from which the azimuth of the corre- 

 sponding" great circle may be read off. The other 

 edge of the protractor carries the usual tangent scales, 

 from which the position of the compass to draw anv 

 circle up to the one corresponding to the cfreat circle 

 makinc an azimuth of zo° with the equatorial plane 

 mav be determined. The scales are based upon a 

 radius of 10 cm. — L. J. Spencer : A (sixthl list of new- 

 mineral names. 



Royal Meteorological Society, March 12. — Mr. C. J. P. 

 Cave, president, in the chair. — R. G. K. Lempfert : 

 Weather forecasts : past and present. For the pre- 

 paration of forecasts, information is now received at 



