Abstract
The velocity of light and the velocity of propagation of radio waves are theoretically identical in vacuo. With refined methods of utilizing radar, long distances can be measured with considerable accuracy. This paper describes the methods used to measure 47 lines varying in length from 67 mi to 367 mi. Six of the lines measured could be compared with geodetic distances obtained from first‐order triangulation. The entire network of lines was so designed that a rigid adjustment could be made. From tie comparison with the six geodetic lengths and from an adjustment of the 41 other lines, a value of the velocity of propagation of radio waves in vacuo is deduced which exceeds lay 16 km/sec the Anderson value of velocity of light in vacuo of 299,776 km/sec. All sources of error are discussed.

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