Eighteen years ago the Department of Terrestrial Magnetism of the Carnegie Institution of Washington, collected radio wave‐propagation data throughout the world during Cruise VII of the research Yacht Carnegie. In 1930 the log‐books of the yacht were examined for high‐frequency radio‐propagation data which were abstracted and summarized.One of the studies undertaken by means of these data was a collection of radio signal‐strengths over long distances in terms of local time at the midpoint of the path of propagation. The reasoning which led to the reference‐time of this path's midpoint was prompted by the fact that the signal‐strength data were collected on a moving observatory. Since the yacht cruised in all oceans and made measurements of signals arriving from all directions, it appeared natural to choose a time‐scale upon which it was possible to represent the information in such a way that any portion of it could be compared with any other part. There resulted a graph of Figure 1.