In July 1991, the world celebrated (about six months early) the bicentennial of the birth of Charles Babbage with a conference at the University of Cambridge and a spectacular exhibit opening at the Science Museum in South Kensington, London. The centerpiece of the exhibit was “Difference Engine No. 2,” the completion of the construction project commenced by Babbage 140 years previously. It was neither a model, a simulation, a replica, nor a reconstruction: the Science Museum, under the direction of Doron Swade, had completed the construction of this calculating machine to the specifications of Charles Babbage, following his original drawings. Aside from the magnificence of the machine as a work of art and as a memorial to the man, this put to an end the myth that Babbage would have been unable to build his machine in the 1840s for the lack of mechanical engineering capabilities. With the help of sponsorship from the Science Museum, ICL (International Computers Limited), Hewlett Packard, Rank Xerox, Siemens Nixdorf, and UNISYS, the machine was manufactured by a small team of engineers who employed the mechanical devices and tools of Babbage’s era, completing the final assembly in full view of museum visitors. Recently, the printing mechanism was completed and added to the exhibit, to fulfill Babbage’s dream of fully automating the calculation and publication of mathematical tables by difference methods.

This new book on the Difference Engine is divided into three major sections, covering Babbage’s work, designs, and tribulations related to the Difference Engine; a section on the Analytical Engine, the major reason for the common assertion that Babbage is the “father of computing”; and an autobiographical section covering the six years of construction of the bicentennial machine. Over the past 25 years, probably more has been written about Babbage in the pages of the Annals of the History of Computing than any other topic, much of it by Alan Bromley of the University of Sydney. Thus much of the contents of the first two sections will be familiar to computer history aficionados, though this presentation is well supplemented by extracts from Babbage’s writing and correspondence.

The third section, “A Modern Sequel,” is the most interesting part of this book. It is an autobiographical story that starts with Bromley’s visit to the museum in 1985 to convince Swade to take on the construction project, and continues with the six years of effort that went into selling the museum the idea of building the machine, validating the feasibility of the project, fund raising, and the detailed construction. This fascinating story, told in the first person, gives details of the problems encountered, the decision making required when forced to deviate from Babbage’s drawings, and the contributions of the many engineers and consultants. As one who was privileged to be a frequent visitor to the museum during this period, and who had the honor of turning the “crank” to compute the square of nine at the opening ceremony, I am delighted that Swade has written this account. The book is really worth reading, both as a historical account of the work of Charles Babbage, and as the record of an enthralling engineering project. After reading the book, visit the Difference Engine!