June 26, 1913] 



NATURE 



441 



lavas and sediments. — J. Parkinson : A group of meta- 

 morphosed sediments situated between Machakos and 

 Lake Magadi in British East Africa. 



Physical Society, June 13. — Prof. C. H. Lees, vice- 

 president, in the chair. — G. E. Bairsto : Some experi- 

 ments on tinfoil contact with dielectrics. This paper 

 describes some experiments showing how the accuracy 

 of the different kinds of electrical measurements that 

 are made on condensers is influenced by the use of an 

 imperfect tinfoil contact. While considerable errors 

 are liable to be made in deducing the specific direct- 

 current conductivity of a dielectric between tinfoil 

 armatures, the same is not true for measurements of 

 the alternating-current conductivity. The influence of 

 the bad contact is twofold. First, it decreases the 

 apparent capacity by inserting in series with the con- 

 denser under test a very large but still finite air 

 condenser. This causes a decrease in the measured 

 conductance. Secondly, because of the decrease in 

 area of contact, it decreases the magnitude of that 

 component of the conductivity which is independent 

 of the frequency — i.e. the purely ohmic conductivity. 

 It is shown experimentally, even under the worst pos- 

 sible circumstances, the dielectric being only lightly 

 bound up with the interleaved tinfoil, that for tele- 

 phonic frequencies the maximum difference between 

 the observed conductivity and true conductivity is 

 15 per cent., and of capacity 5 per cent. With the 

 condenser tightly bound with tape and wedges of wood 

 inserted, the maximum difference was only 4-5 per 

 cent, in the conductivity and 25 per cent, in the 

 capacity. Finally, the influence of imperfect contact 

 upon the accumulation of residual charge is con- 

 sidered.- — G. D. West : A method of measuring the 

 pressure of radiation by means of thin metal foil. 

 The pressure of the radiation emitted by a carbon 

 filament lamp at a distance of a few centimetres is 

 sufficient to cause a microscopically measurable de- 

 flection of the- end of a suspended strip of gold or 

 aluminium foil, and by this means the radiation pres- 

 sure can be calculated knowing the weight of the 

 strip. The results agree to within about 10 per cent. 

 with the energy content per cubic centimetre as 

 measured by the initial rate of rise of temperature of 

 a copper plate exposed to the radiation. The best 

 results are obtained by working in an atmosphere of 

 hydrogen, 1 cm. to 2 cm. pressure, but good results 

 are obtained with hydrogen at atmospheric pressure. 

 Air at 1 cm. to 2 cm. pressure also gives srood results. 

 — Dr. W. Wilson : The emission of electricity from hot 

 bodies and the quantum theory. The paper gives a 

 theory of the emission of electricity from hot bodies 

 which is based on the quantum theory of energy. A 

 formula connecting the thermionic current and the 

 temperature of the emitting body is deduced. This 

 formula closely resembles that of Richardson, and 

 agrees slightly better with experimental results. 



Mineralogical Society, June 17. — Dr. A. E. H. Tutton, 

 F.R.S. president, in the chair. — W. L. Bragg : 

 Crystal-structure as revealed by Rontgen radiation. 

 An analysis of the diffraction patterns obtained when 

 X-rays traverse a section of a crystal shows that in 

 many simple crystals the diffraction is caused by a 

 set of points arranged on a space-lattice. That is the 

 case when the molecule contains either a single heavy 

 atom of at least twice the atomic weight of the other 

 constituents, or only two atoms of nearly the same 

 atomic weight. By comparison of the patterns given 

 by certain alkaline halides, such as KC1 and KBr, a 

 definite structure of these cubic crystals is clearly 

 indicated, and it would appear that the atoms are 

 arranged on a space-lattice the elementary parallelo- 



NO. 2278, VOL. 91] 



piped of which is a cube, alternate atoms being along 

 the axes, so that the atoms of one kind form a face- 

 centred cubic space-lattice. These conclusions are 

 confirmed by a comparison of the distances between 

 planes parallel to the various faces of these crystals 

 carried out by means of the X-ray reflection-spectro- 

 meter, and it appears that a single atom is associated 

 with each point of the space-lattice which diffracts, 

 in the case, for instance, of the alkaline halides, 

 calcite, fluor, blende, and pyrites. If the suggested 

 structure of the crystals is correct, a simple calculation 

 gives the absolute wave-length in centimetres of the 

 homogeneous components in the X-ray beam from a 

 platinum antikathode. — H. V. Ellsworth : The crystal 

 habit of topaz from New Brunswick, Canada. Topaz, 

 a rare mineral in Canada, occurs in York County, 

 New Brunswick, associated with wolframite, 

 molybdenite, and a little fluor. On the crystals the 

 forms no, 120, on, 112, are prominent, but other 

 pyramid and prism forms are sometimes present, 

 sixteen forms altogether being observed. Dull faces 

 were coated with silver by Brashear's process, in 

 which an ammoniacal solution of silver nitrate is 

 reduced by a sugar solution. — Dr. G. T. Prior : The 

 meteoric stone which fell at Baroti, Punjab, India, in 

 September, 191 1. The stone, which belongs to the 

 "intermediate chondrite " group of Tschermak's 

 classification, was found on analysis to contain about 

 9 per cent, of nickel-iron and 7 per cent, of troilite, 

 which were disseminated in small particles through 

 a colourless matrix of enstatite and olivine showing 

 only few chondrules. — Dr. A. W. Gibb : Kammererite 

 from Unst, Shetland Islands. 



Royal Meteorological Society, June 18. — Mr. C. J. P. 

 Cave, president, in the chair. — J. S. Dines : Pilot 

 balloon observations in Barbados, 1911-12. These 

 balloon ascents were carried out by Prof. J. P. 

 dAlbuquerque and other gentlemen, on behalf of the 

 joint upper air committee of the Royal Meteorological 

 Society and the British Association. Great difficulties 

 were experienced in carrying out the work, the most 

 serious of which was due to the adverse effect of 

 the climate of Barbados on the rubber fabric of the 

 balloons, thus causing them to deteriorate more 

 rapidly than in colder regions. Consequently no very 

 high ascents could be obtained. — H. W. Braby : The . 

 Harmattan wind of the Guinea coast. This is a 

 north-east wind which blows during the winter 

 months along the coast of Upper Guinea from French 

 Guinea to the Cameroons. It is exceedingly dry and 

 brings with it fine sand which enters the crevices of 

 doors and windows, covering everything with a film 

 of dust. The sun is partially obscured and distant 

 objects become invisible. This wind, which blows 

 intermittently from November to March, is locally 

 known as "the doctor." — Dr. E. C. Snow and J. 

 Peck : The correlation of rainfall. The authors dealt 

 willi the monthly rainfall from a number of stations 

 in the south-eastern counties of England for the four 

 years iqo8-ii, and found that the rainfall in two or 

 three of the months is more highly associated with 

 that in certain other months than with the rainfall 

 in the remaining months. 



Dublin. 

 Royal Irish Academy, June 9. — Prof. Sydney Young, 

 F.R.S., vice-president, in the chair.— R. Southern : 

 Clare Island reports. (1) Polycliaeta crraniia. In 

 this paper the families Syllidfe to Paraonidas were 

 treated systematically. The total number of species 

 found in these families was 143. Of these, nine were 

 described as new, belonging to the genera Sphaero- 

 syllis (1), Pionosyllis (1), Streptosyllis (2), Opistho- 



