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 REFRACTIONS

BY HENRY PETROSKI

SALVAGING A BIT OF HISTORY

19th-century glass plate technology paved the way for digital projectors.


HENRY PETROSKI - C.P. Snow Predicted China Would Prosper Through Engineering. Last June I visited NASA’s Johnson Space Center in Houston, where I gave a series of lectures based on my book, Success Through Failure. During one of the breaks, a NASA engineer approached me with a grin on his face and a long wooden box under his arm. Even before he reached the lectern, I knew what it was he was bringing to show me.

My book’s first chapter presents a brief history of the projected image and traces the evolution of the technology that made it possible. In particular, I trace the development of the magic lantern from its origins in the 16th century through its epitome in the 19th and on to the overhead, 35-mm slide, and digital projectors of the 20th century.

The emphasis throughout the chapter – as throughout the book – is on how successful improvements were made in response to real and perceived limitations and outright failures in the earlier technology. Invariably, the story of technological development also reveals cultural ties of the present to the past. The images projected by an early magic lantern were painted on glass plates whose height matched that of a slot incorporated into the lantern’s optical system. To change an image, the operator would slide the plate along the slot until the desired image was aligned between the lenses. The plate itself came to be known as a slide. The term persists today in the digital images created and changed within a computer.

The size of lantern slides became standardized in the 19th century (31/4 inches square in Europe; 31/4 by 4 inches in America). With the development of photography came a proliferation of slides, and collections of them grew into libraries. Storage and indexing systems became essential.

An assemblage of glass slides for a scientific lecture could be bulky, heavy, and fragile, and so easy-to-carry slide boxes (known as “slide files”) were developed. A typical box was made of wood, and its inside was fitted with a large number of slots into which the slides could be placed, thus keeping them in order while also protecting them. When the box was opened, the slides were easily selected to be slid one by one into the projector. (Automatic slide changers did exist, but they were not common.)

What the NASA engineer was bringing to the lectern was a file of magic lantern slides. The box was neatly made, but its finish was badly scratched, suggesting that it had seen some use – or abuse. It had a leather carrying handle, which he did not use. He opened the box to show it was almost full of slides. He took one out and held it up to the light to reveal a concept for a space vehicle to leave Earth orbit for the moon. Evidently, NASA was still using lantern slides in its formative years, when we were in a space race with the Soviets. Medical schools and art history departments were also then still using their large libraries of lantern slides of case studies and masterpieces.

The bearer of the slides told me that years earlier he had salvaged the box and its contents from a trash can. Someone had evidently thought them to be of no further value, perhaps because there was no longer a magic lantern available to project them. Or perhaps because they were as unrecognizable as a 51/4-inch floppy disk would be to many students today.

Of course, salvaged artifacts can be invaluable to museums and historians, and I was elated when the engineer gave me one of the slides as a souvenir of my visit to Houston.

Henry Petroski is the Aleksandar S. Vesic Professor of Civil Engineering and a professor of history at Duke University. His book, Success Through Failure: The Paradox of Design is available in paperback from Princeton University Press.

 

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