A simple, all‐purpose oscillator of the negative resistance type called the ``transitron'' oscillator is described. The simplicity of the circuit is such that with the data included herein one may construct the oscillator in a minimum of time and with little effort. Possessing exceptionally good wave form with the attendant efficiency in keeping its frequency from drifting once a definite frequency of oscillation is selected, the oscillator should find favor in general physics laboratories. The versatility of the device lends itself to application in many types of physical research, some of which are described, as well as to the construction of standard physics laboratory apparatus requiring an oscillator as a component part. Use of the oscillator is recommended in medical, biological, psychological, and other fields of research where a source of low voltage at variable frequency is often desired and where the simplicity of the device should be of great help.