In recent years, the problem of seeing through the atmosphere has been given intensive and costly consideration in several quarters, but particularly in the Untied States and Great Britain. A problem which once concerned mainly the meteorologists has become of great importance in military tactics as well as in peacetime transportation. The present volume is the only full account in English of the physical, physiological, and psychological factors which lie at the basis of the calculation of the range of vision through the atmosphere. There is an extended chapter on instruments and one on the author's own theory of the colours of distant objects. The figures are from many sources althrough many of them have been drawn specially for this book. The bibliography contains 420 entries nearly all of which are directly referred to in the text.