e was positioned onto it to make a point contact which acted as a rectifier to detect the signals. These detectors became commonly known as 'cat's whiskers', and were widely used because they were very cheap. Unfortunately they were not very reliable, and often the position of the whisker had to be moved to a better position on the crystal. It was only after the crystal detector was well established that the Audion was used for amplifying signals. It took until 1911 for it to be used in this role, and de Forest quickly exploited the idea when he started to build amplifiers for use as telephone repeaters. As the triode valve started to be used as an amplifier its property to act as an oscillator was very quickly discovered. In fact these early valves were often difficult to stop oscillating, especially at radio frequencies. This was put into good use in a number of ways. As far as radio reception was concerned it soon led to the development of the regenerative receiver. Here positive feedback in the circuit was used to increase the sensitivity and selectivity, although the circuit was main- tained just before the point of oscillation for the best performance. The American Edwin Armstrong is normally credited with this invention, although others including de Forest, Irving Langmuir in the USA, and Alexander Meissner in Germany also discovered the idea at about the same time. In 1914, war broke out. With this, wireless research on both sides of the conflict took on a new degree of urgency as its importance was recognized. In developing new and better receivers many famous engineers including H.J. Round, Latour, and Edwin Armstrong on the Allied side and W. Schottky for the Germans devoted vast amounts of research effort into the development of better techniques. Although the idea of the regenerative receiver had given significant improvements over anything that was previously available, receivers still lacked the performance which was sought. Many of the limitations were caused by the poor performance of the valves.