To those engaged in the art of communication nothing is more striking than the revolutionary developments which are taking place in telephony, especially in the conversion of switching to a mechanical basis and in the remarkably rapid extension of long distance communication. These developments are due in the first place to the fact that prompt and accurate interchange of ideas by means of speech is a primitive and fundamental need in human intercourse. To whatever extent means for satisfying this need are made available, they will be accepted and used by the community, provided always that the cost is not exorbitant. It is the realisation of this fact that has justified the very large amounts expended in financing the developments now taking place. Yet finance alone is not sufficient to bring about these great advances. It is progress on the technical side that has made it possible for telephone administrations thus to extend their activities. Technical progress has been made in two ways: first, in the application of scientific methods of study to the performance of telephone plant and, second, in the development of new and improved materials and manufacturing processes.