Vannevar Bush's seminal paper is available from a number of web sites.

I first read it on paper in Michael Fraase's "Macintosh Hypermedia", Scott, Foresman Ltd, 1989 ISBN 0 673 38791 7. While lots of the technical stuff in Michael Fraase's book is now out of date it still worth reading for information about the historical development of hypermedia and some of his ideas about the nature of the medium.