MEASUREMENTS of the horizontal velocity of travelling disturbances in the F2 region of the ionosphere have been made in this department over the past three years, using the method described by Munro1. Constant-frequency pulse transmitters were set up at the base station in the Physics Department of the University of Western Australia, and at two other stations situated respectively 15 miles east and 25 miles south-east. The two remote stations were triggered, after a short adjustable delay, by the ground wave from the University transmitter. Three sets of echoes were obtained at the base station, one reflected vertically from overhead and the other two at oblique incidence from the mid-points between the remote stations and the base. They were recorded on the one film by the conventional techniques. The frequency used was 5.8 Mc./s. and the pulses were 100 µsec. long with a pulse repetition frequency of 40 c.p.s.