May 20, 1920] 



NATURE 



375 



of the country if shown flat. The pictures should be 

 «.-nlarged to an equivalent focal length greater than 

 th<.' uistance of distinct vision, and mounted in a 

 polygon circumscribing a circle of radius equal to the 

 local length. 



The Meteorological Office: New instruments and 

 diagrams : (i) Land aneroid and sea aneroid. 

 (2) Barometer with micrometric adjustment. (3) Two 

 similar synchronous charts and the weather of the 

 following fifteen days. (4) Normal weather on the 

 Cairo to Cape route. (5) Charts of the average dis- 

 tribution of rainfall, cloudiness, and temperature over 

 the northern and southern hemispheres in January 

 and July. (6) Map of the annual rainfall in the 

 English Lake District. (7) Records of the magnetic 

 disturbance of March . 23-^4, 1920, and photographs 

 of aurora for height-measurements. (8) Frequency of 

 thunderstorms on the route between England and 

 Australia and at selected stations in Africa and South 

 America. (9) The flow of air over Kew Observatory, 

 Richmond, during the last three years. 



Air Ministry Laboratory : Apparatus for air naviga- 

 tion, (i) Four alternative methods for the quick 

 solution of spherical triangles necessary for the ob- 

 taining of position lines from astronomical observa- 

 tions taken from aircraft : (a) The d'Ocagne nomo- 

 gram. (6) A slide-rule based thereon, (c) The Veater 

 diagram, (d) The Bygrave slide-rule. (2) Wimperis 

 wind-gauge bearing plate, to enable the velocity and 

 direction of the wind to be measured whilst in flight, 

 (!) by flying on two courses and noting the drift 

 angles, and (ii) by flying on one course and using a 

 chronometer. (3) Capt. Weir's (Littrow projection) 

 diagram applied to the purpose of obtaining position 

 lines from W/T bearings. 



The Admiralty Compass Department: (i) Two 

 standard types of aircraft compasses. (2) Examples of 

 aperiodic compasses for use in ships and aircraft. 

 The aperiodic system adopted in these compasses is 

 a result of the investigations of Mr. G. T. Bennett 

 and the late Lt.-Comdr. C. Campbell. 



Mr. E. A. Reeves: Apparatus for showing the exist- 

 once of a true north and south directive force in the 

 electricity of the atmosphere. This apparatus con- 

 sists of a large glass bottle with an india-rubber 

 stopper, from which is suspended by a fibre of un- 

 spun silk a gold-leaf paper indicator. The inner side 

 of the stopper is covered with paraffin wax, and the 

 bottle is coated inside and out with shellac varnish. 

 The whole is mounted on a tripod stand. On a calm, 

 clear day, when the apparatus is set up in a high 

 open space and screened from the direct rays of the 

 sun, it is found that after the paper is electrified bv 

 touching it with vulcanite rubbed on dry cloth, and 

 left for some time, it will oscillate about evenly on 

 either side of the true north and south line, or come 

 to rest approximately in that direction. 



Mr. C. V. Boys: (1) Noon reflector. The noon 

 reflector is a very simple form of transit instrument 

 intended to be set on a window-sill facing south and 

 producing a pinhole-reflected image of the sun on the 

 ceiHng or opposite wall, from which the time may be 

 obtained with an accuracy of about one second. 

 (2) Azimuth declination time-chart. The azimuth 

 declination time-chart is a graphic representation of 

 the hour angle of the sun for all declinations at a 

 particular latitude and azimuth from which the hour 

 angle may be read with an accuracy of one-tenth of 

 a second of time. This is for use with the noon 

 reflector w^hen set at some azimuth other than 30uth. 



The National Physical Laboratory : Oriented lustre 

 of etched crystalline surfaces. The etched crystalline 

 surface of metal is covered with a number of minute 

 plane facets the orientation of which is uniform 

 throughout each individual crvstal, but varies from 

 NO. 2638, VOL. 105] ^ 



one crystal to the next. A beam of oblique light fall- 

 ing on such a surface is selectively reflected by these 

 facets in such a way that the area of certain crystals 

 appears uniformly and brightly illuminated, while 

 other crystals remain dark. By illuminating such a 

 surface by means of three separate beams of coloured 

 light falling upon the crystals at various angles of 

 incidence a striking effect is produced. Each crystal 

 reflects into the eye of the observer a portion of one of 

 the beams falling upon it at a suitable angle, and the 

 various crystals consequently appear of different 

 colours (Dr. W. Rosenhain and Mr. J. H. Haughton). 



Messrs. Adam Hilger, Ltd. : Vacuum grating 

 spectrograph for the extreme ultra-violet. A concave 

 grating spectrograph, specially designed for the 

 investigation of the Schumann and Lyman regions 

 of the s}x>ctrum. No refractive substance {e.g. 

 quartz or fluorite) is introduced, but the whole spec- 

 trum is obtained with one setting of the grating by 

 the use of two slits. These are disposed in the end 

 plate of the instrument, just above the plate-holder, 

 which is cylindrical in form and provided with a plate 

 for sealing purposes. 



The Osmosis Co., Ltd. : Clays treated by electro- 

 osmosis : Photomicrographs and specimens of articles 

 made with osmosed clay. The phenomena of elec- 

 trical osmosis, whereby matter in a very finely divided 

 state is capable of being influenced by an electrical 

 potential, have an important practical use in the puri- 

 fication of clays. Low-grade and discoloured china 

 clays becorne usable as paper clays and pottery clays» 

 and all china clays are improved in colour as a result 

 of treatment. 



Messrs. J. Crosfield and Sons, Ltd. : Synthetic pro- 

 ducts for perfumery. Synthetic perfumes of British 

 manufacture w'ere shown, most of which were for- 

 merly produced entirely in foreign countries. The 

 manufacture w^as undertaken owing to the difficulty, 

 in some cases impossibility, of obtaining such products 

 during the war. 



Mr. A. Mallock: Apparatus used in the determina- 

 tion of the variation of rigidity with temperature. 

 The specimen to be tested forms part of a torsion 

 balance, in which the restitutive couple is supplied by 

 the torsion of a long thin wire, together with that of 

 the specimen, the latter being in the form of a short 

 wire or narrow strip about 2 in. long. The specimen 

 and lower part of the balance can be immersed in a 

 tube of fluid kept at any desired temperature. The 

 periods of oscillation are automatically recorded for 

 various temperatures, and the ratio of these periods 

 furnishes the necessary data for determining the ratio 

 of the rigidities. In rnnking an experiment the oscil- 

 lations are maintained continuously, the specimen 

 being immersed successively in water at 100°, at 

 room-temperature, in carbonic acid, in alcohol, and 

 in liquid air. 



Mr. C. R. Gibson for Mr. Joseph GooJd: Experi- 

 ments in rotational dynamics. The exhibit illustrated 

 is a new development of Mr. Goold's earlier experi- 

 ments in vibrating bars, the most remarkable of these 

 being the vortex phenomenon demonstrated about a 

 quarter of a century ago. The new experiments 

 showed a rotational effect which is independent of 

 the vortex phenomenon. A light clamp is fitted across 

 the steel bar carrving an upright needle or rod. upon 

 the free end of which is supported a light metal vane 

 or "spinner." On settiner the plate in vibration the 

 soinner rotates with considerable energy. This rota- 

 tion results from the interplay of two systems of vibra- 

 tion acting at right angles to each other. The fol- 

 lowing explanation is suggested by Mr. Gibson, who 

 gave the demonstration : In one of the systems the 

 bar vibrates between nodal lines which cross the 

 width of the bar: this is terme<l a normal system. 



