266 



NATURE 



[June 5, 1919 



It will be remembered that Prof. Eddington and 

 Mr. Cottingham were provided with the 13-in. 

 object-glass of the astrographic telescope of the 

 Oxford University Observatory, whilst the 

 observers in Brazil had *he similar object-glass 

 from Greenwich, and that the programme at both 

 stations was to take photographs of the stars 

 that surrounded the sun, of which there are at 

 least twelve within 100' of the sun's centre of 

 photographic magnitude ranging from 4*5 to 7'o, 

 for the purpose of testing Einstein's relativity 

 theory of gravitation, and also the hypothesis that 

 gravitation, in the generally accepted sense, acts 

 on light. Photographs that have been taken 

 during the eclipse will be compared with others 

 that have been, or will be, taken of the same stars 

 in the night sky to detect any displacement that 

 may be considered to be due to the presence of 

 the sun in the field. 



There is at present no information as to the 

 type of the corona, and apparently few observing 

 parties have been organised to make observations 

 to record this. From a note in the daily Press 

 last week, said to emanate from the Yerkes 

 Observatory, it seems not unlikely that a large 

 prominence may have been on the limb of the 

 sun at the time of the eclipse. 



It had been announced that the Cordoba Ob- 

 servatory would dispatch an expedition to Brazil, 

 and that possibly Prof. Abbot, of the Smith- 

 sonian Institution, would proceed to La Paz, 

 Bolivia, where the eclipse happened at sunrise, 

 with coronal cameras and with instruments for 

 measuring the sky radiations by day and night, 

 but it is too early to have heard of any results of 

 such observations. Also it has been announced 

 that Prof. D. P. Todd would take photographs 

 of the eclipse from an aeroplane at a height of 

 10,000 ft. from the neighbourhood of Monte 

 Video, where the eclipse would only be partial. 



As to experiments other than astronomical, the 

 actual programme arranged by the British Asso- 

 ciation Committee for Radio-telegraphic Investiga- 

 tion, the object of which was given in Nature of 

 May 8, was that the sending-stations at Ascension 

 and the Azores with others in America should 

 send letters of the alphabet at intervals from 

 iih. 30m. (G.C.T.) until i4h., and that any 

 observers who would take part in the experiment 

 should record these and their strength by a 

 number according to a scale familiar to wireless 

 telegraphists. A scheme for making special mag- 

 netic and allied observations during the eclipse 

 was organised by the Department of Terrestrial 

 Magnetism of the Carnegie Institution under the 

 direction of Prof. Bauer, with stations at (i) La 

 Paz, Bolivia, (2) Huancayo (north of belt of 

 totality), (3) near Sobral, Brazil, (4) Prince's 

 Island, and other stations outside the belt of 

 totality if possible. The reports of the observa- 

 tions of this kind that have been made will be 

 given as soon as possible, but much cannot 

 be said until published results arrive from 

 America. 



NO. 



2588, VOL. 103] 



WIRELESS TELEPHONY. 



MARCONI'S Wireless Telegraph Co., Ltd., 

 . gave a very interesting demonstration of 

 the latest developments of wireless telephony at 

 its works at Chelmsford on May 28. Although 

 there was nothing very new from the scientific 

 point of view, yet the developments in engineer- 

 ing design were remarkable, especially in. the re- 

 ceiving apparatus. Many of the devices proved 

 of the utmost value to the Army during the 

 war. We were impressed with the portable 

 wireless telegraph station for use with pack or 

 wheeled transport. Six men are required to work 

 the set, and the whole station can be erected in 

 ten minutes. The masts are of steel, 30 ft. in 

 height, and a single horizontal aerial is used, the 

 earth connection being made with strips of metal 

 gauze placed on the ground. The generating set 

 consists of a two-cylinder, 2f-h.p. petrol engine, 

 which drives a high-frequency |-kvv. alternator. 

 The "instrument load " consists of transmitting- 

 valves, high-frequency transmitting-circuits,^ 

 microphone, etc., all contained in a teak travel-* 

 ling-case. 



To work the apparatus, the petrol engine is 

 started. This drives the high-frequency alter- 

 nator. The current generated is carried to the 

 transmitting-circuits, where it is transformed by 

 a series of transformers. The final transforma- 

 tion raises the potential to 10,000 volts; the 

 current is then rectified by a Fleming valve and 

 converted into a continuous-wave current by a 

 system of condensers and choke coils. This 

 current energises the aerial circuit, where a large 

 fraction of the power is radiated off into space. 

 For the transmission of speech the amplitude of 

 the oscillations generated in the aerial is varied 

 by a microphone into which the operator speaks. 

 The microphone acts on a transformer connected 

 in the grid circuit of the transmitting-valve. 



The receiver consists of a simple tuning 

 arrangement which is connected to the aerial. 

 The oscillatory currents produced by the received 

 signals are amplified by a series of oscillatory 

 valves. The last of the valves rectifies the cur- 

 rents and feeds the telephones through a suitable 

 transformer. Conversation between the two 

 stations is then carried on in exactly the same 

 way as in ordinary telephony. 



For normal flat country the guaranteed range 

 for telephone transmission is 60 miles, but com- 

 munication can sometimes be made over 120 

 miles. For continuous wave (C.W.) transmis- 

 sion the guaranteed range is 200 miles. A 

 demonstration of the working of the apparatus 

 was given, and conversation was carried on as 

 easily as over an ordinary telephone line. 



Amongst other devices shown were the wireless 

 telephone apparatus used in aeroplanes with the 

 pendent aerial and the windmill generator. Very 

 large high-power spark generators for long- 

 distance transmission were shown in action. A 

 demonstration was also given of telephonic com- 



