An announcement of this published by the Vorwarts says that it 
would probably be necessary to forgo the publication of the fourth 
volume, which was to contain the history of the theory: 

“apart from a few notes, no preparatory material for the concluding volume of 
his work has been found”. 

We hope that the Vorwärts is somewhat mistaken in this. At any 
rate F. Engels presents us with a rather less hopeless piece of 
information in the Preface to the second volume of Capital. 
According to this, a manuscript dating from the years 1861-63, A 
Contribution to the Critique of Political Economy comprising 1,472 
quarto pages, contains (pp. 220-972) a section entitled ‘Theories 
of Surplus Value”, of which Engels says: “This section contains a 
detailed critical history of the pith and marrow of Political Economy, 
the theory of surplus value... After eliminating the numerous 
passages covered by Books II and III, I intend to publish the 
critical part of this manuscript as Book IV.”* 

a See present edition, Vol. 36, Engels’ Preface.— Ed.