The reconsideration Opened out upon some suggestions for the use of entropy as a meteorological element in various ways that invited exploration. In particular it has been found possible to regard an isentropic surface as a practical alternative for sea-level or some other horizontal surface on which to place the facts about weather. Only the beginnings of the exploration have been made and it is hoped to enlist the reader's assistance in its prosecution. To break off that exploration in order to include the recital of the achievements of Newtonian dynamics in the domain of meteorology would be a change of key-note more suitable for another volume, to include what has already been printed in Part Iv, than another chapter which would leave Part IV as a detached appendix. The new volume is the more natural since the original Part IV is already out of print.
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