For years I used many of the same slides in my introduction to structures course, a course that is partly about design, partly about analysis and partly about the history of bridges. Since I have argued that design is a timeless pursuit, I believe that its principles can be illustrated equally with old and with new case studies.
However, the frontiers of bridge building are ever changing, and I want students to be up-to-date. To keep my lectures current, I had to supplement my historical slides with new ones taken at construction sites or newly completed structures or with ones from other sources.
To keep the duration of my lectures within the classroom period, I could run through the older slides more quickly, although this would defeat my purpose of giving the students more than a superficial survey of historic bridges. Or I could take out one slide of an old bridge every time I added an image of a new one, leaving students unexposed to a historically significant structure.
This is a familiar dilemma faced by historians, and it somewhat explains why textbooks for survey courses tend to grow in size over time. To keep them within the physical bounds imposed by the limits of bookbinding technology—and by the wallet—authors and publishers have to constantly weigh the costs and benefits of retaining enough detail about the old to make its recounting more than a too-thin slide show projected at a too-fast pace.
It is seldom easy to design a course that strikes the right balance. Many a faculty member teaching material at the forefront of his or her field seems compelled to sacrifice the history for the present, apparently thinking it is more relevant to the future. This is short-sighted, I believe, for if there is one constant running through the development of every technology, it is change. Concentrating on the present to the exclusion of the past eliminates an opportunity to discuss how technology evolves. It is like trying to determine the slope of a curve from a single point on it. Calculus, one of the indispensable tools of engineering, teaches us that to calculate the instantaneous change of a quantity, we need to know something about its past or its future.
The history of a field is what provides that data, and usually over such a relatively long period of time that we can see patterns of change, periods of growth and decline, cycles of progress and retrogression that might not be evident in the span of a single career. An appreciation of the way technology evolves is invaluable for engineers pushing the frontiers of their chosen field into uncharted territory.
Sometimes researchers in emerging disciplines look at a field like structural engineering as a closed book, one in which everything that needs to be known is known. Of course, those working on the design and construction of record-setting bridges know that this is simply not true, as vibration problems with the latest cable-stayed spans demonstrate. The surest way to prepare future engineers for those surprises is to expose them to surprises of the past. That is why so much of what I teach involves failures.
Last fall, as I looked ahead to teaching my course again, I realized that the slides I had used in the past not only contained the lessons of history but also embodied old technology. This semester I am converting my lectures from 35-mm slide shows to PowerPoint presentations, not to change the message but the medium, lest my students mistake old technology for old ideas.
Henry Petroski is the Aleksandar S. Vesic Professor of Civil Engineering and a professor of history at Duke University. His latest books are “Pushing the Limits: New Adventures in Engineering” and “Success Through Failure: The Paradox of Design.”