Excerpt: For half a century, threshold has been known to be important in the activities of nerve cell and synapse, but little is known of the general properties that so ubiquitous a feature must impose on the system’s behaviour in the large. Beurle1, in his investigations of the transmission of waves of activity over a conducting not, noticed that a net with threshold would have a marked tendency to be unstable, but his assumptions were complex, and the origin of the instability is not easily identified. Here we propose to show that an instability, similar to his, can readily be traced from a simpler origin.

This paper describes a method for presenting on a fluorescent screen the time varying velocity and density modulation of an electron beam, modulated at a frequency of 3000 Mc, as it emerges from the cavities of a klystron, the wave guide in a traveling wave tube, or similar structures. In order to deflect an electron beam at this frequency, each pair of the usual deflection plates is replaced by a two‐wire transmission line, resonant at the beam modulating frequency. Under proper phase conditions a circular trace is obtained, where one complete revolution of the beam corresponds to exactly one complete cycle of events on the beam at the point of its deflection. Since electrons having different velocities will be deflected differently, a complete velocity and density picture of the beam at a given point of interest is obtained. This is demonstrated by observing the bunching action in the drift region of a velocity modulated electron beam.