Continual measurements of the horizontal and vertical components of eddy motion have been made on the 420-foot meteorology tower at Brookhaven since early 1950. The equipment used for this purpose is an all-weather, remote-recording bivane. Numerous tests have been conducted to determine the characteristics of this instrument, both on the tower and in a wind tunnel. Initially, it was tested and used with a flat-plate, tail section; more recently, it has been tested and used with an annular-fin tail assembly.