A description is given of the Seismoline, an electrical analog computer of theoretical reflection seismograms involving all primary and multiple reflections. The computer utilizes an analogy between seismic wave propagation through a stratified earth and electrical wave propagation along a lumped-parameter transmission line. A description is given of the prototype Seismoline and the experimental tests performed on it. It is concluded that it provides a convenient, speedy, and sufficiently accurate computer for the quantity production of theoretical seismograms, except possibly in cases where the acoustic impedance contrasts of the geologic section are extremely low. Changes in the velocity and thickness of the various geologic layers may be made with ease, and the resulting changes on the seismogram can be viewed almost simultaneously. This inherent flexibility introduces the possibility of a feedback process whereby an operator might modify his filter settings or the geologic model in order to effect a better match between corresponding theoretical and field seismograms.