It was my privilege to give the Newmarch Lectures for the academic year 1948-9 at University College, London. In preparing them for publication I have thought it best to leave the topics in their original order, but not to divide the text of this essay into four sections corresponding to the individual lectures. The ground covered by each of these is contained in Sections I-VI, VII-XIII, XIV-XXI, and XXII-XXIX respectively, and the only extensions I have made are as follows. The topics of Sections VI and x were barely touched upon in the lectures themselves and are expanded here. The numerical illustration of Section XVI has been revised in the light of the national income White Paper which appeared in April 1949 and a detailed explanation of the way in which these figures have been derived has been added. Time did not permit any reference to the details of Section XVII or to the studies described in Sections xxvn and XXVIII.

I am indebted to two members of the Department of Applied Economics for the help they have given in preparing this book for publication. Section VI has benefited from the criticisms of Mr J. Durbin and I was assisted in the presentation of Section x by Mr S. F. James.

The temerity of attempting to cover so large a subject in so small a space is obvious. For the benefit of any who may wish to pursue the various topics further I have included a number of references, mostly to the literature of the last decade. The list is in no sense comprehensive; it contains simply those books and articles which have seemed to me most relevant among those I happen to have come across.