TO SWIM a mile and back at two miles an hour takes sixty minutes. But if one swims it down with, and up against, a mile-an-hour current, one mile is made at three miles an hour, taking twenty minutes, and the other at one mile an hour, taking sixty minutes. The time for the round trip is thus increased one third because the slower progress is made over a longer period than the faster progress.
Similarly, when a bomber flies to an objective and back, there is always a net loss in bombing radius if a steady wind exists. The average condition is no more favorable than a steady wind. Bombing radii must therefore be somewhat discounted and, as the fact seems so generally overlooked, it may be interesting to see what the usual effects amount to.
By formula III, we may produce the following table: