July 14, 1923] 



NA TURE 



71 



parallel to the plates past the same conductor. By 

 the use of exploring electrodes connected to telephones 

 through a three-valve audio-frequency amplifier, it 

 is possible to determine positions of the electrodes 

 which reduce -the sound in the telephones to a mini- 

 mum, and hence obtain the equipotential lines of 

 the system, or the stream-lines for the case of fluid flow. 



In the Engineering Department a new method of 

 testing the efficiency of gear - boxes was shown in 

 which the difference of the input and output powers 

 is measured directly and not as a difference. The 

 method consists of the observation of the torque 

 produced as a consequence of the difference of the 

 input and output powers when the gear-box was 

 supported in a tilting frame. Apparatus was shown 

 for the study of explosions in closed vessels. This 

 has an important application in the design of internal 

 combustion engines where it is desirable that the 

 explosions should occur under the most favourable 

 conditions of temperature and pressure of the mixture. 

 This is, of course, largely influenced by the compression 

 ratio, which is, however, limited in effect by detonation 

 or " knocking " at high compression ratios. 



In connexion with the experimental study of roads 

 and road materials a new plant for the preparation 

 of bituminous macadam was exhibited. The plant 

 consists of two units, one for mixing sand, etc., at 

 a temperature of 600° F., and the other for mixing 

 the aggregate with bitumen. It is capable of mixing 

 about six tons of road metal per hour. Other ex- 

 hibits included apparatus for the investigation of 

 fatigue under uniform bending moment, and its 

 correlation with the microstructure of the material ; 

 the endurance of ball-bearings under axial loading ; 

 and the hardness of materials as tested by their 

 ability to resist scratching by a diamond. 



The main exhibit in the William Froude National 

 Tank was the method of determination of the stresses 

 liable to be set up in the rudder heads of ships when 

 the rudder is altered in certain definite ways. The 

 problem is one on which attention was focussed 

 during the War, when even with vessels which were 

 classed Ai at Lloyd's damage to stearing gear was 

 of much more frequent occurrence than was antici- 

 pated. For this purpose a ship model capable of 

 independent motion and external control was under 

 observation from the travelling carriage of the tank, 

 and the effect of putting the helm over at various 

 rates and through different angles investigated. 

 The experiments show that it is possible to add more 

 than 50 per cent, to the strain on the rudder head by 

 changing the helm too quickly. 



Other exhibits included apparatus for determining 

 the stresses on a rudder behind a fin plate with twin 

 screws, and for the determination of the resistance, 

 rise, and angle of seaplane models in motion. 



In the Metrology Department standard weights 

 were exhibited. In this connexion it is interesting 

 to note the experiments of the Laboratory on a new 

 material, stellite, as a substitute for platinum for 

 standard weights. Stellite, which is an alloy of 

 chromium, cobalt, and tungsten, is exceedingly hard, 

 and tests made on these weights show that it has 

 great promise as a platinum substitute. The weights 

 liave been under observation for two years, and have 

 liown that stellite possesses great stability ; weights 

 made of it remaining constant to less than i part 

 m 10,000,000 over that period. 



A new gear-measuring machine was also exhibited ; 



with this machine it is possible to measure the pitch 



of teeth, tooth-shape, and thickness, concentricity 



if teeth with the gear axis, parallelism of teeth with 



1 he axis, radial symmetry of teeth, and the pitch 



liameter. By ingenious arrangements " the profile 



NO. 2802, VOL. 112] 



of the successive teeth can be magnified and made 

 visible on a smoked glass and examined by projection 

 methods, while the variation from uniform motion 

 of two gears in mesh can also be critically examined. 



A travelling microscope, in which many of the 

 errors prevalent in the usual form of travelling 

 microscope are eliminated, was demonstrated. In 

 addition, the instrument, by suitable gearing, gives 

 results simultaneously in inches and centimetres to 

 a ten-thousandth of an inch or centimetre. 



The exhibits in the Electrotechnics Division in- 

 cluded the experimental arrangements for precision 

 resistance measurements, for research on buried 

 cables, for the determination of the errors of current 

 transformers, and for the photometric measurement 

 of lamps. An interesting demonstration of the 

 attraction of the suspended particles in oil to electrodes 

 at high potentials showed how such impurities can 

 diminish the insulating properties of oils used for 

 insulating high-tension apparatus. The illumination 

 building in which experiments on the window 

 efficiency of rooms are carried out was also open 

 for inspection. 



The end hardening of gauges, which was in- 

 vestigated in conjunction with the Metrology Depart- 

 ment, was also shown here. The gauge is made 

 one electrode in a furnace and passes a heavy current 

 through a piece of graphite, which is thereby heated 

 to a high temperature. The portion of the gauge in 

 contact with the graphite thus attains a temperature 

 considerably above the critical temperature for steel, 

 and on dropping into water all the portion which 

 was above the critical temperature is very effectually 

 hardened. In this way only a very small proportion 

 of the material of the gauge is interfered with in the 

 hardening process. 



The Wireless Division's exhibits consisted of 

 apparatus for measuring both the direction and 

 intensity of the electro-magnetic field from a distant 

 radio transmitting station, and for applying these 

 measurements to the study of the propagation of 

 electro-magnetic waves over the earth's surface. To 

 assist in this study of radiation problems, a trans- 

 mitting station using both damped and undamped 

 waves has been erected. An earth screen is em- 

 ployed at this station with various forms of antennae. 

 Apparatus was also shown for the absolute measure- 

 ment of the amplification produced by a valve 

 amplifier at audio - frequencies : this is used for the 

 testing and investigation of both valves and their 

 coupling transformers. 



In the Radiology Division a Bragg spectrometer 

 was shown in operation for the examination of the 

 structure of metals and alloys. The method is a 

 modification of the powder method of determining 

 crystal structure, and has been extended to several 

 systems of alloys, including copper and aluminium, 

 copper and nickel. In each case it is found that in 

 solid solution the solute atom enters into the lattice 

 of the solvent by substitution. The structures of 

 such metallic compounds as CuAlj and AgMg have 

 also been determined by this method. Apparatus 

 consisting of a spherical ionisation chamber for the 

 investigation of the scattering of X- and 7-rays was 

 also shown. This problem is of interest in connexion 

 with deep therapy treatment using X- or 7-radiations, 

 where, unless suitable precautions are taken, it is 

 possible to obtain several times the desired exposure 

 due to the scattering effect of surrounding tissues. 



In the General Physics and Heat Divisions the 

 exhibits were mainly of apparatus for determining 

 the thermal constants of materials. Among these 

 were a special calorimeter for use with substances 

 that react with water, new forms of immersion 



