384 SECTIONAL TRANSACTIONS.— G. 



Monday, September 14. 



Mr. H. F. Shanahan. — Electricity for the consumer (10.0). 



Prof. E. W. Marchant. — A note on the operation of a variable oscillator 

 for speech frequencies, with an iron cored choke (11.0). 



A demonstration using a dynatron form of oscillator, in which the 

 inductance in the tuned anode circuit was of the iron-cored type. The 

 variation in frequency is effected by varying the grid bias on the oscillator 

 valve. In this way a range of nearly 4- 1 in frequency could be obtained. 

 The wave shape of the oscillations as shown by cathode ray oscillograms 

 approximates to a sine curve, at the higher frequencies. The oscillator was 

 applied to a vibrating monochord and could be used to exhibit the modes 

 of vibration of the monochord, when the frequency was varied continuously 

 over a considerable range. 



Mr. A. W. Ladner. — Beam wireless. The beam array, developments in 

 design and influence on long-distance communication (11.20). 



Preliminary. — Chief difficulties of short-wave communication are fading 

 and echo, and, until array systems were used, short waves were of no value 

 for commercial communication. 



Arrays. — Practical beam arrays were first developed for Imperial wireless 

 and were of the broadside type. These arrays consist of a long line of 

 ' in-phase ' radiators giving maximum directivity normal to the line. 

 Vertical directivity being a function of height, high arrays were necessary 

 for efficiency, and thus broadside arrays have a high prime cost. 



Gain of arrays. — The gain of a broadside array is 10 per square wave- 

 length, and if arrays are used at both ends of a system, the total gain is 

 the product of the gains each end. Thus a system having 10 square wave- 

 length arrays each end would give a gain of 10,000, and early arrays 

 approached these figures. 



Developments. — By phasing the currents along an array line it is possible 

 to bias the directivity to a direction in line with the array. In this case 

 directivity in all planes is a function of length, and hence efficient arrays 

 of low height can be built. This effects great economy in cost, and most 

 modern arrays are of the ' in line ' type. 



The influence of the array on communication history. — Before beam 

 wireless, overseas communication was by submarine cable. Great Britain 

 had achieved a virtual monopoly of overseas communication owing to our 

 possessing so many islands and countries dotted over the world, which 

 materially assisted the growth of a cable network. Long-wave wireless 

 had failed to compete with cable communication, but the beam established 

 an immediate high-speed long-distance service, much above the needs of 

 the time. Immediate results were the Government-sponsored merger of 

 Cables and Wireless in Great Britain. But beam wireless was available to 

 all countries, and the growth of foreign competition is slowly breaking 

 Great Britain's monopoly of overseas communication. 



Dr. F. W. Lanchester. — Magnetic and electric units (12.0). 



