A brief review of literature on devices furnishing negative resistance is made and further possibilities of development indicated New names are suggested for negative circuit constants. It is shown that for transient states the negative inductances and negative capacitances respond as would be expected of true negative circuit constants. External circuits are suggested to vary the negative resistance of a given vacuum tube system. A system of circuits is described by means of which it is possible to obtain impedences proportional to ±(jω)n, where n is any positive or negative integer.