The ionospheric sounder and its place in the history of radio science

It is suggested that Breit and Tuve's 1925 application of pulses to ionospheric sounding, which led to the most widely used form of radar, also gave rise to a scientific instrument whose utility, flexibility, and general suitability for intended applications place it on a par with such familiar and standard devices as the telescope or spectrograph. By way of background, there is included a discussion of the circumstances attendant upon the first measurement of ionospheric layer height, which took place in 1912.