56 



NATURE 



[January 12, 1922 



A Notable Exhibition 



'pHE Physical Society of London and the Optical 

 A Society held their t\yelfth exhibition of elec- 

 trical, optical, and other apparatus at the Imperial 

 College of Science on January 4 and 5. As in past 

 years, the exhibition rooms were crowded with ap- 

 paratus and visitors ; the latter were so numerous 

 that the exhibition became a continuous one instead 

 of closing between 6 and 7 p.m. each day. The 

 display of scientific apparatus was probably the finest 

 ever seen in this country, and the quality and finish 

 of the instruments left little to be desired. There 

 were many instruments of novel design, but attention 

 can be directed to a few only. 



A quite novel exhibit was an optical sonometer 

 by the firm of Hilger, Ltd. This is designed 

 to record the pressure variations caused by 

 sound-waves, and should prove invaluable to 

 w^orkers in acoustics. The most novel feature 

 is the diaphragm, which is a film having a 

 thickness of a fraction of a wave-length of light, 

 and is silvered or gilded on one side by a cathode 

 process. The sound-wave under examination is 

 received by a horn, and causes the diaphragm, 

 and ultimately a beam of light, to vibrate. An intense 

 point image is produced, and a photographic record 

 can be obtained on a rotating film. The vowel sounds 

 and all kinds of acoustic disturbances may thus be 

 analysed. In another arrangement, which is excel- 

 lently adapted for demonstration purposes, a rotating 

 band with white lines on a dark ground is illuminated 

 by a line image from the diaphragm. By adjustment 

 of the speed of rotation stationary wave effects are 

 obtained. 



The episcope, shown by Newton and Co., is a 

 marked improvement on forms previously seen, and 

 should come into more general use for the projection 

 on screens of opaque objects. The present instru- 

 ment is of beautiful design, and with its two 2000- 

 candle-power lamps very bright pictures of opaque 

 objects may be projected on a screen 5 metres or 

 more away. In large teaching institutions this instru- 

 ment could be put to many uses. 



The Marconi Co. exhibited its new automatic 

 alarm which responds to the wireless call of a ship 

 in distress. In the present form of instrument the 

 distress call must consist of three dashes, each of 

 four seconds' duration, the dashes being separated by 

 oiie-second intervals. ^ By means of an amplifying 

 circuit, plungers working in dash-pots are caused to 

 respond to the four-second impulses, and after a 

 series of three such impulses a warning signal 

 occurs. If the impulses last for more or less than 

 four seconds, subject to a tolerance of about half a 

 second, the circuit necessary to operate the alarm is 

 not completed. The demonstrations given were 

 accompanied by artificial atmospherics and con- 

 tinuous wireless reception, and were remarkably 

 successful. 



Creed and Co. again showed their system of high- 

 speed automatic printing of wireless messages, but at 

 an increased S|>eed of reception. Signals from 

 Chelmsford were regularly received, the Morse code 

 perforations in a paper strip being transposed into 

 Roman characters by an automatic printer. The 

 speed ranges from 50 to 200 words per minute. 



of Physical Apparatus. 



While the writer was present a message was received 

 from the Marconi Co. conveying its wishes for the 

 success of the exhibition. The receiving aerial ap- 

 peared to be a very insignificant affair, and many 

 visitors marvelled at the present efficiency of triode- 

 valve amplifiers. 



A novel weather foreteller, the design of which is 

 due to Mr. Kitchen, was shown by Negretti and 

 Zambra. The instrument is based on meteorological 

 data extending over many years. The forecast for 

 twelve hours appears irt a small window in the instru- 

 ment after the barometer and wind-scales have been 

 set to correspond to the conditions existing at the 

 time. It would be of interest to have a record over 

 six months of "predictions " and "happenings." 



Tucker's hot-wire resonator microphone was shown 

 by H. W. Sullivan. The microphone consists of a 

 heated wire in the neck of a resonator and is insensi- 

 tive to all but the particular sound frequency which 

 it is desired to receive. The hot wire is cooled by 

 the oscillating air-currents at the resonant frequency, 

 and the change in the resistance of the wire is caused 

 to operate an amplifier. 



The Cambridge and Paul Instrument Co. exhibited 

 a novel temperature regulator, in which the current 

 from a thermo-couple in a furnace passes through 

 a millivoltmeter, at the end of the pointer of which is 

 a light thermo-couple in series with a moving coil 

 relay. When the furnace is at the temperature which 

 it is desired to maintain, the light thermo-couple 

 is brought, by the movement of the pointer, into close 

 juxtaposition to a small heated body. A current is 

 thus generated which ojjerates the relay and in- 

 directly controls the current in the furnace. The 

 instrument exhibited controlled a small electric fur- 

 nace at about 700° C. within about 5° C. 



The Edison Swan Co. showed a 10,000-candle- 

 power pointolite lamp of ingenious construction ; 

 many visitors remarked on the skill required to seal 

 leads into glass for the passage of a current of 40 am- 

 peres. The firm of Ilford, Ltd., showed a new and im- 

 proved colourless filter which completely cuts off ultra- 

 violet rays. It is claimed to be much superior to the usual 

 aesculin filter, and is known as "Q" (acetamino- 

 quinoline). The Davison microteJe scope, while not 

 new, attracted considerable attention, and users of 

 the microscope admired a new 25-watt mercury vapour 

 lamp made bv Chas. Baker. Shotter's integrator for 

 water-flow meters vi^as shown byH.Tinsley; it repre- 

 sents a new application of the Wheatstone bridge. 

 Among precise measuring instruments the Campbell 

 fundamental standard of mutual inductance (shown 

 bv R. W. Paul) must be mentioned, and also the 

 "Talymin," by Taylor, Taylor and Hobson, which 

 determines within small limits of error the outside 

 diameters of small manufactured parts. 



An experimental lecture on "The Johnsen-Rahbek 

 Electrostatic Telephone and its Predecessors " was 

 given on both days by Mr. A. A. Campbell Sv^'inton. 

 Another lecture on " Radium : Its Apolication in 

 Peace and War " was delivered bv Mr. F. Harrison 

 Glew, and a third lecture on "The Employment of 

 Coarse Wire Gratings in Astronomy " was given by 

 Sir Frank W. Dvson. These lectures were attended 

 by large audiences, and were highly appreciated. 



'T*HE twenty-second annual general meeting of the 

 ■*• Science Masters' Association, which was held 

 last week at the Imperial College of Science, was 

 presided over by the Master of Balliol. His address 

 on the subject of the relationship of history and 

 NO. 2724, VOL. 109] 



Science in Secondary Schools 



science will long be remembered by those who were 



fortunate enough to hear it for the genial humour and 

 literary grace with which he defined the position and 

 imf>ortance of these complementary branches of 

 learning. 



