IONOSPHERIC absorption measurements by pulse reflexion at vertical incidence were resumed at Ibadan, Nigeria (latitude 7° 26′ N, longitude 3° 54′ E, mag. dip 6° S), in 1966, using frequencies of 2.0–7.5 MHz and taking measurements as far as possible in accordance with the recommendations for the IGY1. Similar measurements were made at Colombo (latitude 6° 54′ N, longitude 79° 52′ E, mag. dip 5° S) between 2.0 and 5.4 MHz. Colombo and Ibadan have almost the same geographical latitude and magnetic dip, but differ in longitude by about 76°. The effect of the difference in longitude is discussed here.