A description is given of the basis and method of calculation of the new table of refraction included in the Air Almanac for 1943 onwards; the table caters for heights up to 55,000 ft. and all altitudes above the visible horizon.

As already announced the Air Almanac and the American Air Almanac will become a single publication, under the title of the Air Almanac, as from 1953. To cater for the greater heights at which aircraft now fly, and for the possible use of observations at very low altitudes, the refraction table has been completely redesigned. The explanation of the table in the Almanac is naturally restricted to instructions for and illustrations of its use, and, in view of the current interest in refraction, especially at low altitudes, it seems desirable to place on record a full description of the theoretical basis of the table and of the method by which it was calculated.