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These new features - speech amplification, call signalling device and keysetimpulsing - are characteristic of the telephone sets for electronic systems whichare now at an advanced stage of study. Amplifying and active units must beprovided for calling and impulsing, the former because an electronic exchangecannot send ordinary ringing current but only v.f. current. It was therefore anatural step to introduce transmitter amplification as well. As is seen fromfig. 1, the requirement of material is fairly large.Loudspeaking telephones have every prospect of a bright future. Theirdesign is perhaps not yet ideal, but when they have been perfected in thatrespect at a reasonable cost, they should find their way to many homes.As regards the external design of telephone sets, the fifties have been arevolutionary period. Coloured sets have become common - most being ofthermoplastic. In U.S.A. there are two-colour sets, the case and handset beingof different colours, so avoiding the differing discolouration of these twoparts during the life of the set. The fifties saw the birth of the Ericofon,which has been very well received by subscribers. During the sixties peoplemay well come to think of the telephone as an integral part of the furnishingof their home. Administrations and manufacturers must be prepared to providethe public with elegantly designed sets in many different colours, and to adapttheir colour range to the dictates of fashion. We may have to produce newtypes of set fairly often. There is even a risk that less scrupulous manufacturerswill sell telephones direct to subscribers for plugging into their wall sockets.Line PlantThe line plant is the most costly part of a telephone network. Creditableefforts have been made to reduce this cost. The principal items are cable andinstallation work. The main striving has been to lower the cost of cable andwire through use of the new materials that have become available. Secondly,methods of installation have been rationalized. And only in the third place havetechnical developments been drawn upon for the modernization of linematerial such as cable fittings, protective equipment etc.During the fifties plastic cables took a big stride forward. This tendencymay be expected to continue during the sixties, line materials being successivelyadapted to suit plastic cables.For local line plant, even in the forties, 0.4-mm wire began to oust largergauges of wire wherever the attenuation conditions permitted. A furtherdevelopment in this direction-to 0.3-mm wire-is proceeding in some places.The problems of manufacture and jointing are troublesome, since 0.3-mmwire is rather fragile. The line equipment must also be reconstructed to fitthe new wire.The replacement of copper by aluminium in local cables does not appearso attractive. From the attenuation point of view this would often be possible,but aluminium is difficult to joint. It also involves problems of manufacturebecause of its lower strength and ductility. Considerable changes in cablemakingmachinery would probably be necessary. Aluminium cables arethicker than copper cables, moreover, which is undesirable in local plant.Any general change from copper to aluminium will depend on the price factor.