204 



NA TURE 



[June 28, 1906 



and the ends immersed in liquid air. Tlie relative con- 

 ductivities are as the squares of the height of the ice 

 columns, (c) Spheroidal state of liquid air on the surface of 

 different fluids and solutions, showing changes of volatility 

 from the varying amount of vapour condensation ; at the 

 same time exhibiting interesting rotatory and translatory 

 movements. — Department of Applied Mathematics, Uni- 

 versity College, London: (i) Investigation into the stresses 

 in masonry dams, Prof. Karl Pearson, F.R.S., and Mr. 

 A. F. C. Pollard. The investigation suggested that the 

 shear distribution should in each case be found from a 

 model dam, before the stresses are determined by graphical 

 methods. The existence of stretch in the tail of dams of 

 ordinary type is confirmed by the experiments illustrated, 

 ul .Solution of the problem of the random walli, Prof. 

 Karl Pearson, F.R.S., and Mr. J. Blakeman. The 

 diagrams shown give the sections of the frequency surface 

 for two, three, four, five, six, and seven stretches or 

 flights, and show the passage of the discontinuous function 

 into Lord Rayleigh's continuous surface. The problem is 

 of considerable importance from the standpoint of the 

 migration of species, and was suggested by Major Ross's 

 investigations into the infiltration of mosquitoes into a 

 cleared district. The solution has been obtained by suc- 

 cessive mechanical integration from the first case bv using 

 the functional relation between successive flights. — Mr. 

 A. A. C. Swinton : Visibly luminous electrical discharges 

 1" vacuo obtained with comparatively low electrical pres- 

 sures. Edison, Fleming, and others have shown that the 

 passage of the electric discharge in vacuo is much facili- 

 tated by heating the kathode. Owen and VVehnelt have 

 proved that this effect is enormously increased if the heated 

 kathode be coated with oxides of the alkaline metals. The 

 present experiments show that similar results can be 

 obtained by coating the kathode with radium, and that the 

 effect will be greater when the kathode is heated than 

 obtains without heating. — Mrs. Watts-Hughes and Mr. 

 Richard Kerr : Floral, geometric, and other forms produced 

 by the human voice in singing. Moistened water-colour is 

 spread on paper attached to an india-rubber disc stretched 

 over a cup-shaped vessel. The sound vibrations are com- 

 municated to the under side of the india-rubber through a 

 tube in the side of the cup. — Mr. Oliver S. Dawson : 

 Photographic prints in natural colours (.Smith-Merckens 

 process). — Messrs. Carl Zeiss, Jena : Photomicrographic 

 apparatus for ultra-violet light (designed bv Dr. A. 

 Kohler). 



Mr. R. G. Durrani: Evidence to show that ionic separ- 

 ation occurs when solutions of acids or of salts are allowed 

 to diffuse into sensitised jellies or solutions. — Dr. O. 

 Silberrad and Dr. R. C. Farmer: Stability test for cordite. 

 This exhibit illustrated a method recently devised at the 

 Chemical Research Department, Royal Arsenal, Woolwich, 

 for the determination of the stability of cordite and other 

 propellant explosives. It is well known that these ex- 

 plosives decompose gradually on storage, and may 

 eventually ignite spontaneously, if their stability be not 

 tested from time to time. The principle of the new test 

 is based upon the results of several thousand experiments, 

 and is the only method known which gives trustworthy 

 results with cordites. The test has been adopted by the 

 Service, and will shortly be made use of as a safeguard 

 against spontaneous e.xplosions in powder magazines, par- 

 ticularly in the tropics, where the deterioration takes place 

 rnost rapidly. In examining cordites the procedure is 

 briefly as follows : — 50 grams of the explosive are main- 

 tained at 70° C. in a glass vessel fitted with a mercury 

 manometer ; the alteration in pressure is measured at 

 intervals. A contraction takes place at first owing to the 

 absorption of oxygen from the air ; .subsequently agradual 

 expansion occurs ; the former of these phenomena has never 

 previously been observed. — Dr. F. D. Chattaway : Copper 

 mirrors obtained by the deposition of metallic copper upon 

 glass. The method of silvering glass by depositing the 

 metal in a thin film by reduction of some soluble silver 

 compound has long been employed in the production of 

 mirrors, but hitherto no method of similarly depositing 

 copper in a brilliant film has been discovered. ' The exhibit 

 showed a number of glass vessels on which copper had 

 been thus deposited by a slow reduction of the black 



NO. I913, VOL. 74] 



oxide. The metal being protected from the air, such 

 mirrors retain their lustre permanently. 



Mr. G. F. Herbert Smith : Precious stones and simple 

 methods for their identification. This exhibit illustrated 

 the variety of precious stones which are available for 

 ornamental purposes. .-^ gem stone must be hard enough 

 to resist the abrasive action of ordinary dust, and at the 

 same time be either transparent or, if opaque, of pleasing 

 colour. The number of mineral species suitable for the 

 purpose is not so restricted as popularly supposed. The 

 names employed by jewellers frequently differ considerably 

 from the scientific nomenclature, being often associated 

 with certain colours rather than particular species, e.g. 

 topaz (yellow), sapphire (blue), ruby (red), emerald (green), 

 and amethyst (violet). The colour, though the most obvious 

 character of a stone, is the least trustworthy ; and the 

 hardness, while of immense importance as regards its 

 durability, is of little discriminative value. On the other 

 hand, the optical characters (refractivity, double refraction, 

 and dichroism) and the specific gravity may be easily and 

 accurately determined, and lead to the precise identification 

 of the stone. In the case of practically all faceted trans- 

 parent stones the refractivity and double refraction are 

 sufficient for the purpose, and the stone need not be re- 

 moved from its setting. — Sir William Crookes, F.R.S. : 

 (i) Occurrence of the diamond. (a) Example of " blue 

 ground " in which diamonds are found, from the 1320-feet 

 level, De Beers Mine ; (b) diamantiferous gravel from the 

 Pulsator, De Beers Mine ; (c) selected stones from the 

 Pulsator, De Beers .Mine. (2) Models of crystals of 

 diamond. (3) Cut and polished section of a piece of 

 silicified wood found about twelve years ago in the un- 

 touched " blue ground " of the Du Toits Pan Diamond 

 Mine, Kimberley. (4) Polished section of the Canon Diablo 

 meteorite in which diamonds have been found. — Prof. W. 

 Gouiland : (i) Portion of a meteorite containing diamonds 

 found near Carton Diablo, Arizona, and specimens of 

 diamonds extracted from it. (2) Alloys of copper and 

 calcium. A series of alloys ranging from 0-8 per cent, to 

 61-5 per cent, of calcium. .All are brittle, and those con- 

 taining 6 per cent, to 7 per cent, calcium extremely hard. 

 The higher alloys decompose water, and are readily oxidised 

 in the air. Specimens were also exhibited showing the 

 effects of calcium on lead, tin, bismuth, aluminium, and 

 coinage bronze. — Miss Rhodes : Stereoscopic views of the 

 Victoria Falls and the Batoka Gorge of the Zambezi, and of 

 the Batoka country east of the Falls. Photographed by 

 the late Colonel F. W. Rhodes. 



The Director, Royal Gardens, Kew : Sturt's desert pea 

 (Clianthus Dampieri). A prostrate herbaceous plant, 

 native of West Australia, first collected by Captain William 

 Dampier. Under cultivation it is very delicate, but when 

 grafted on the bladder senna (Colutea arborescens) it grows 

 with vigour and flowers freelv. — Dr. F. E. Fritsch : 

 Method of colonisation of free surfaces by subaerial .Alga; 

 (Cyanophycese) in the tropics. — Mr. E. A. Newell Arber, 

 Miss M. Benson, Miss W. Brcuchlev, Prof. F. W. Oliver, 

 F.R.S., Dr. D. H. Scott, F.R.S., and Prof. F. E. Weiss: 

 Fossil plants from the English Coal-measures. — Mr. W. 

 Saville-Kent : Stereoscopic and other natural-colour photo- 

 graphic transparencies illustrating the fauna of the Poly- 

 nesian coral reefs. This series of natural-colour photo- 

 graphs was more particularly illustrative of the coral- 

 frequenting fishes of Polynesia. A notable genus of mostly 

 minute percoid fishes. Tetradachnum, represented in the 

 series, habitually make isolated bushy coral stocks their 

 headquarters. They cruise around these coral growths 

 in sport and in search of food, retreating within the 

 coral's ramifications to rest or to escape from any 

 enemy. 



The Solar Physics Observatory, South Kensington : 

 Recent photographs of some British stone circles. — Dr. 

 W. M. Flinders Petrie, F.R.S. : (i) Hyksos fortress model, 

 and pottery, 2000 B.C., Egypt. (2) Model of the temple 

 and city of Onias, Egypt. (5) Photographs, enlarged, from 

 Sinai. The Egyptian turquoise mines were worked from 

 5000 i!.c. The oldest rock sculptures are those of the 

 middle of the first dynasty of kings. Both centres of 

 mining, Wady Maghara and Serabit el Khadem, were 

 shown. 



