May 19, 192 1 J 



NATURE 



377 



'The Royal Society Conversazione. 



THE first conversazione this year of the Royal 

 Society was held at Burlington House on 

 May II, and was attended by a large number of 

 fellows and guests, who were received by the presi- 

 dent. Prof. C. Sherrington, and the officers of the 

 society. Many exhibits of objects and apparatus of 

 scientific interest were shown, and we have grouped 

 together those on related subjects in the subjoined 

 summaries of some of them from the descriptive 

 catalogue. 



Prof. K. Onnes, Sir R. A. Hadfield, and Dr. H. R. 

 Woltjer : Apparatus and specimens used in research 

 on the influence of low temperatures on the magnetic 

 properties of alloys of iron with nickel and man- 

 ganese. A series of iron-manganese and iron-nickel 

 alloys was exposed to the temperatures of liquid air, 

 liquid hvdrogen, and liquid helium respectively and 

 the specific magnetism tested after return to atmo- 

 spheric temperatures. Tests were also made during 

 immersion in liquid hydrogen ( — 253° C). The alloys 

 with the higher percentages of manganese cannot be 

 made magnetic even by immersion in liquid helium 

 ( — 269° C). The existence of one magnetic and one 

 non-magnetic manganese-iron compound is shown to 

 be probable. 



Messrs. Evershed and Vignoles, Ltd. : Needham's 

 pulsator system of speed measurement and control. 

 This system provides a sensitive electrical means of 

 measuring speed, and may be employed as a speed 

 telegraph of a novel and extremely trustworthy char- 

 acter. In addition to signalling from one or a number 

 of control positions, measurements may be effected 

 simultaneouslv and independently at a number of 

 positions, so that the system is one of great flexibility. 

 It also indicates the direction of rotation. The system 

 is extremelv suitable for use on ships, in power 

 stations, and in other places where the measurement 

 or indication of speed is desired at a distance from 

 the moving machinery 



Tlic Hon. Sir Charles Parsons and Mr. Stanley S. 

 Cook : .\n attempt to reach high instantaneous pres- 

 sure by the collapse of a hollow sphere of lead under 

 external pressure suddenly applied bv an explosiv^e. The 

 sphere is made up of two hemispheres placed together 

 with tissue-paper between and soldered around the 

 periphery of the joint. In the cavity is placed the 

 substance to b# compressed. If its final diameter in 

 nuclear form is i/20oth that of the initial hollow, and 

 the pressure of the explosive 20 tons per square inch, 

 the nuclear pressure produced is 1,000,000 tons. The 

 explosive is fired in six places simultaneously. 



Cambridge and Paul Instrument Co., Ltd. : Ap- 

 paratus similar to Mr. C. T. R. Wilson's original 

 cloud expansion apparatus, but improved by Mr. T. 

 Shimizu so that o-, ^3-, and X-rays may be con- 

 tinually demonstrated. 



Mr. E. A. Griffiths: Liquid oxygen vaporiser. 

 The liquid oxygen is contained in a metal vacuum 

 vessel. The emission of gas is governed bv bringing 

 a flexible portion of the outer wall into contact with 

 the inner, the degree of contact determining the 

 rate of transmission of heat across. The bottom of 

 the outer vessel is a corrugated plate of silver to the 

 centre of which is soldered a copper block shaped to 

 fit the contour of the inner vessel. The displacement 

 of the diaphragm is controlled bv a screw. Any 

 desired rate of gas evolution can be obtained up to 

 10 litres per minute, and the delivery remains con- 

 stant with any particular setting for several hours. 



Mr. J. St. \nncent Pletts : The Davis-Pletts slide 

 rule. In this slide rule the log-'og scale and its 



NO. 2690, VOL. TO7] 



reciprocal scale are related to the log scale in such 

 a way that the numbers on the latter are the common 

 logarithms of the numbers opposite them on the 

 former. This enables full advantage to be taken of 

 the properties of characteristics and mantissas for the 

 purpose of indefinitely extending the non-recurring 

 log-log scales. Further, scales for all the ordinary 

 exponential, circular, and hyperbolic functions are- 

 arranged to read on the same log scale, so that any 

 product or ratio of such functions can be obtained. 

 Thus all such compound functions as e^ sin a and 

 log a cosh X can be obtained with a single setting of 

 the slide and cursor, while every combination of the 

 various functions is obtainable with two or more 

 settings. 



The National Physical Laboratory: (i) Radio- 

 telegraphic direction-finding apparatus (Mr. R. L. 

 Smith-Rose). This apparatus is of the tvpe developed 

 by Capt. Robinson, of the Royal Air Force. Instead 

 of finding two positions of a receiving coil for which 

 the signals have equal intensity, two coils at right 

 angles are connected in series and rotated together 

 until the signal strength is unaltered by reversing the 

 connections of one of them. This gives the direction 

 from which the signal is coming, and, therefore, the 

 apparent bearing of the transmitting station. Differ- 

 ences between the apparent and the true bearing are 

 found to occur, especially at night ; these differences 

 raise many interesting questions in connection with 

 the transmission of electro-magnetic waves in radio- 

 telegraphy. (2) Resistance alloy "omal" for elec- 

 trical standards (Dr. W. Rosenhain, Mr. S. W. 

 Melsom, and Mr. S. L. Archbutt). The material is 

 of the type usually known as "manganin," and is an 

 alloy of copper, manganese, and nickel. Prior to the 

 war the product was supplied almost exclusively by 

 Germany, and great difficulty was experienced by 

 makers of scientific and ordinary measuring instru- 

 ments in obtaining material suitable for their pur- 

 pose from any other sources. The question was in- 

 vestigated at the laboratory, and as a result alloys 

 were made and watched through the various pro- 

 cesses that meet the requirements as regards tem- 

 perature coefficient, constancy, resistivity, and secular 

 change. The material is made in two t\pes, one 

 having a resistivity of 45 michrom-cm. and the other 

 of T? michrom-cm. Samples of the product are shown 

 in various stages of manufacture in the form of cast 

 ingots, rod, strip, and wire, together with micro- 

 graphs and curves of temperature coefficient. (3) 

 Relay for breaking moderately large electric currents 

 (Dr. Guv Barr). The difficulties due to sparking at 

 the contact of ordinary relays are avoided by causing 

 the make-and-break to occur between mercury elec- 

 trodes in an atmosphere of hydrogen. An iron core 

 floating in mercury carries at its upper end a silica 

 cup, also full of mercury. Connections are made to 

 the mercury outside and inside the cup. A solenoid 

 pulls the core and cup down and thus makes the con- 

 tact ; the current is broken by the core floating up 

 so that the surface of the mercury is cut by the silica. 

 The spark is sufficiently quenched to allow currents 

 UP to 20 amperes at 100 volts to be broken easily. 

 The mercury remains clean, (a) Standard optical 

 pyrometer (Dr. Kave and Dr. Griffiths). This instru- 

 ment has been designed with the view of facilitating 

 the accurate measurement of high temperatures bv 

 the "disappearing filament " method. An image of 

 the hot object is superimposed on the filament of the 

 pyrometer lamp and the brightness matched by var\-- 

 ing the current through the lamp. Monochromatic 



