Part 1 of the paper gave an account of the measurement of the velocity of propagation of centimetre waves over a sea path at low level, and concluded that the velocity is 186,217±16 miles/sec. Part 2 gives the results of experimental flights observed from two Oboe ground stations in order to measure the velocity of propagation as a function of height above the earth. The results indicate higher velocities than those previously calculated. The most probable values for the mean velocity of propagation between ground and aircraft at 10,000, 20,000 and 30,000 ft are 186,233, 186,246 and 186,256 miles/sec respectively, the metric equivalents being 299,713, 299,733 and 299,750 km/sec respectively.