INTRODUCTION

The equations developed in Ch. 4, between the integrated quantities represented by the capital letters P, R, ME, MN, hold good, with the approximations indicated, for any one of the conventional strata. But in the stratum, which has its base at 11·8 km and extends upwards to at least 40 km, the ratio of pressure is so great that the aforesaid approximations are all open to criticism and must be reexamined. This examination is one of the principal aims in Ch. 6. Another aim is to find a way of extrapolating observations made by balloons, which seldom penetrate into the upper tenth of the mass of the atmosphere, so as to obtain P, R, ME, MN which are integrals up to the top. The final aim is to choose a set of quantities, either P, R, ME, MN or some other equivalent ones, and to find a corresponding set of equations so that, when the quantities are given at one instant, the equations will give their time rates. This problem is for the most part carried over to Ch. 8. But its general features have already been described in Ch. 4/0.

The quantities P, R, ME etc. are the definite integrals of p, ρ, mE etc. with respect to height, taken so as to include the whole thickness of the stratum.