The Velocity of Radio Waves over Short Paths

The velocity of radio waves was measured directly in the following manner. Two radio stations were set up on frequencies of 3492.5 and 2398 kilocycles, respectively. One station was fixed while the other was portable. The fixed station sent out pulses which were received at the portable station. A thyratron control set off return pulses which came back to the base station. At the base station the two pulses appeared upon a cathode-ray oscilloscope with a sweep of 22,800 inches per second. The separation of these pulses gave the time for the pulses to travel twice the distance between the stations plus the time required to pass through the receiving apparatus. By taking the portable station to two positions one 0.73 kilometer from the base and the other 3.67 kilometers, it was possible to eliminate the time lag in the receiver and so to find the exact time of propagation. Each station was in sight of the other. The average of 180 measurements was 2.985X10
¹⁰
centimeters per second.