62 



NATURE 



[May 19, I. 



Three photographs, taken with some of the plates, were ex- 

 hibited. 



Dr. Armstrong, F.R.S., exhibited coloured photographs of 

 Yellowstone Park, U.S.A., by Mr. F. Jay Haynes, of St. Paul, 

 Minn.; Mr. A. E. Tutton, an interference dilaton-.eter of in- 

 creased sensitiveness; and Mr. Edwin Edser, apparatus exhibiting 

 peculiarities of interference fringes when formed between silvered 

 surfaces. When interference bands similar to Newton's rings 

 are formed with monochromatic light between two partially 

 silvered surfaces, the appearance presented is that of narrow 

 sharply defined bright bands separated by broad dark intervals. 

 When the light used consists of two different wave-lengths (such 

 as that from a Bunsen burner into which some salt of sodium has 

 been introduced) the interference bands become alternately 

 double and single as the distance between the silvered surfaces 

 is increased. This principle has been used by MM. Fabry and 

 Perot to confirm Michelson's results as to the homogeneity 

 or otherwise of- spectral lines incapable of resolution by spectro- 

 scopic methods. 



Mr. Edwin Edser and Mr. C. P. Butler showed a simple inter- 

 ference method of calibrating a spectrometer. Two pieces of 

 plate glass, each thinly silvered on one surface, are placed with 

 these surfaces parallel and very nearly in contact. This arrange- 

 ment is placed immediately in front of the collimator slit of a 

 spectrometer. A ray of slightly convergent white light being 

 directed on the slit through the air film between the silvered 

 surfaces, the resulting sj^ectrum consists of bright bands 

 separated by dark intervals. If the wave-lengths corresponding 

 to any two interference bands l)e known, that corresponding to any 

 other band can be calculated or determined graphically with 

 great accuracy. It is proposed to use such a system ot inter- 

 ference bands as a reference spectrum, to facilitate the reduction 

 of prismatic spectra in terms of wave-lengths. 



Prof. W. C. Roberts- Austen, C.B., F.R.S., exhibited appar- 

 atus to illustrate M. Daniel Berthelot's interference method of 

 measuring high temperatures. One of the beams of light in an 

 interference apparatus traverses a heated porcelain tube, and the 

 other beam traverses a tube of equal length containing rarefied 

 air. When interference takes place it indicates that the air in 

 the two tubes is equally rarefied., and therefore the temperature 

 of the heated tube can be calculated from the pressure of the air 

 in the other tube. The interference apparatus employed is that 

 exhibited by Messrs. Edser and Stansfield at the conversazione 

 last year. Prof. Roberts-Austen also showed a complete instal- 

 lation of apparatus for the microphotography of metals. 



Mr. A. Stansfield exhibited (i) experiments of showing an ex- 

 ception to the law of Magnus ; (2) a method of demonstrating the 

 existence of an allotropic change in iron. An electric current 

 may be generated by heating unequally a circuit compos-id of a 

 single metal, if very steep temperature gradients are maintained 

 in the wire of which it is composed. The Thomson E.M.F. 

 must therefore be abnormal under these conditions. Experi- 

 ments were arranged to demonstrate this in the case of platinum 

 and other metals, and to show readily the allotropic change 

 which takes place in iron at about 800" C. 



Dr. Alexander Muirhead and Prof. Oliver Lodge, F.R.S., 

 showed improvements in Hertz-wave space-telegraphy ; Prof. 

 Ewing, F. R. .S., a magnetic balance for permeability tests of 

 iron; Mr. J. E. Stead, specimen and photographs illustrating 

 the crystalline structure of iron and steel ; and Mr. Joseph 

 Goold, experiments in relation to resonance. 



An exhibit by the Hon. C. A. Parsons consisted of (i) one 

 of the earlier Parsons steam turbines of three-horse power 

 driving a dynamo ; speed of working, 12,000 revolutions per 

 minute; (2) photographs of the Turbinia ; (3) screw propeller 

 cavitating the water, the atmospheric pressure being removed 

 from the surface by an air pump. A small screw propeller is 

 driven by an electric motor at a speed of iocK> revolutions per 

 minute within a tank in the form of a hollow oval ring, around 

 which the water flows under the action of the propeller, the con- 

 ditions of flow resembling closely those in the case of an 

 ordinary screw propeller driving a ship. The illumination is 

 effected by a beam from an electric lam]> reflected from a mirror 

 attached to and rotating with the screw shaft, and again reflected 

 on to the propeller by a concave fixed reflector. The propeller 

 thus illuminated appears stationary, and the cavities in the 

 water formed by and around the blades can be clearly seen or 

 photographed. To facilitate the formation of cavities, and to 

 reproduce the conditions of very fast ships at convenient speeds 



! for observation, th^ whole of the atmospheric pressure is re- 

 moved from the upper surface of the water by an air-pump. The 

 \ pressure then remaining to hold the water together, is that die. 

 to the head of water above the screw, plus capillarity. The xt- 

 lation holding between the model and screws on fast ships, wi h 

 the same slip ratio, when cavities are formed appears to be— 

 lineal speed of , bla<^e varies as the square root of the total 

 pressure holding, the water together. 



Prof. W. A. Herdman, F.R.S.,and Prof R. Boyce, exhibited 

 healthy and unhealthy green oysters, showing the causes of the 

 coloration, and the connection between oysters and disease. 



The Marine Biological Association had an exhibit showing 

 the adaptations of marine animals to their environment, illustra:ed 

 by living examples of the higher Crustacea. 



The Jo.int Permanent Eclipse Committee and Eclipse Com- 

 . rnission of the British Astronomical Association showed photo- 

 ; graphic and other observations made in India at the total solar 

 ■eclipse of 1898, January 22. 



Prof. Sherrington, F.R.S., exhibited specimens of sensorial 

 organs, illustrated by the microscope. 



Sir Richard T. Thome, F.R.S., and Dr. Copeman had an 

 exhibit illustrating the bacteriology of calf vaccine lymph. 



Mr. Horace Seymour, Deputy Master of the Mint, exhibited 

 a case of medals bronzed by Japanese methods. Various solu- 

 tions are employed by the Japanese for this purpose, but 

 " rokusho," or verdigris, is the main constituent of most of 

 them. The medals shown are the result of experiments inade in 

 the Mint with a view to reproduce Japanese effects. 



Dr. Russell, F. R. S. , showed pictures taken on photographic 

 plates by vapours from certain metals and certain organic 

 bodies. 



Sir David Salomons, Bart., exhibited the pseudoscope for pro- 

 ducing stereoscopic effects by means of a single picture. 



Prof. Unwin, F.R. S., exhibited apparatus for indentation 

 tests of metals. The relative hardness is measured bj the in- 

 dentation per ton per inch of knife edge. 



Dr. MacMunn showed microscopic preparations illustrating 

 the structure of the digestive gland of Mollusca and Decaped 

 Crustacea. 



Electrical recording apparatus was shown by Pro.". H. L. 

 Callendar, F.R.S. 



Mr. C. T. R. Wilson demonstrated production of cloud by 

 the action of ultra-violet light. When the light from an arc 

 lamp is brought by means of a quartz lens to a focns within a 

 vessel containing moist, dust-free air, a bluish fog gradually 

 develops along the path of the light. The effect is entirely 

 prevented if the ultra-violet rays be cut off by interposing a 

 sheet of glass or mica, no cloud or rain resulting under these 

 conditions even when supersaturation is brought about by sudden 

 expansion. Possibly the small particles which give rise to the 

 blue of the sky are produced by the ultra-violet rays of sunlight 

 absorbed in the upper layers of our atmosphere. 



Prof. Oliver Lodge, F.R.S , exhibited improvements in mag- 

 netic space-telegraphy. The discharge of a condenser or Leyden 

 round a large wire coil sets up an alternating magnetic field, 

 which excites induced currents in another distant c ndenser- 

 circuit tuned to the same frequency, causing the second Leyden 

 either to overflow into a coherer, or to disturb a Rutherford 

 detector or a telephone so as to give a signal. 



The detector shown was a special series of small free coils and 

 granular microphones, each coil in a permanent magnetic field 

 and so connected to the microphone of the next that a very 

 feeble alternating current in the first of the series is able to 

 make a telephone in the last emit a loud sound, or, through a 

 Langdon-Davies relay, to ring an electric bell and work a Morse 

 sounder. A tone-telephone was also shown, which acts as a 

 highly syntonised " call." 



The magnetic vibrations in the sending current can be main- 

 tained in various ways, but the way shown is a device due to 

 Dr. Papin, with a vibrating string and battery contact. A sig- 

 nalling key enables the ordinary Morse alphabet to be sent 

 without any connecting wire, and independently of obstacles. 

 It may be regarded as, in some respects, a modification and im- 

 provement of the induction method of telegraphy inaugurated 

 by Mr. Willoughby Smith and practised by Mr. Preece ; but, 

 with suitable circuits, the tuning must be nearly exact to evoke 

 much response, and with enough copper in each circuit there is- 

 no assignable limit of distance. 



Prof. A. Barr and Prof. W. Stroud exhibited range-finders. 



NO. 1490, VOL. 58] 



