Propulsion and Paradigms

David Stone, senior member of the solid earth group in the Geophysical Institute, once told me that geologists had to adopt a new motto: "If I hadn't believed it, I wouldn't have seen it."

That wry twist on the old cliche acknowledges the revolution in geology brought by the theory of plate tectonics, commonly called continental drift. Such changes of the basic world view in a scientific field are now called "paradigm shifts." Geology isn't the only discipline to have its paradigm shift. Darwin nudged biologists into seeing living things through the lens of evolution; physicists had to yield Isaac Newton's gravitational force to Einstein's curving space-time. Those are truly major changes of paradigm, but of course little ones come along too. The shift is simply the way science progresses---"by leaps and stumbles," to quote another of Stone's informal observations.

Technology, where science is applied to everyday life, sometimes sees paradigm shifts also. Refinements appear in an existing technology, it gets better and better, but suddenly Wham ! Something different leaps (or stumbles) past it. Consider, for example, a form of transportation Henry Petroski writes about in a recent issue of American Scientist: powered transoceanic ships.

Early in the last century, by the time Britain and America quit battling for good and concentrated on trading, a swift sailing vessel blessed with good weather might cross the Atlantic in as little as three weeks. With less benign conditions, the crossing might take eight weeks or even more.

More speed would mean more money to the traders, so they were willing to encourage experiments. An early one was the steamship Savannah. In 1819, she made the voyage from Georgia to Liverpool in just under four weeks. The traders were not impressed. Savannah had been powered by steam for only 85 hours out of that voyage, because that was all the coal she could hold---and coal and ballast was all she carried. Sacrificing cargo and passengers to space for holding fuel and machinery did not appeal to ship owners. The conventional wisdom---the paradigm---held that no vessel would ever be able to carry enough fuel for the entire journey. To cross the ocean, ships needed sails.

That paradigm shifted in stumbles. In 1833, the larger Royal William made the crossing from Nova Scotia to London in 25 days with eight passengers and some cargo aboard. Bigger was better; that voyage nibbled at the conventional wisdom. But because the Royal William's boilers used sea water, every fourth day she proceeded under sail while the crew cleaned salt from her boilers. Calculations had shown that ship size was a crucial factor, but experience proved that it wasn't the only one.

Half again bigger than Royal William and equipped with condensers to recycle fresh water for her boilers, Great Western crossed the Atlantic in 15 days during the spring of 1838, but she carried only seven passengers. Nevertheless, she turned a profit. The conventional paradigm was almost dead. Under power alone, economically competitive vessels were crossing the Atlantic.

Decades later, after propellers had replaced paddlewheels and iron hulls become more common than wooden ones in the proliferating steamers, a new paradigm had replaced the old one. Power vessels had shrunk the seas. All that remained to do was refine the technology, making ships bigger, faster, safer, more luxurious. That trend peaked in 1952 with the launching of United States, a liner just under 1000 feet long, capable of carrying 2000 passengers in luxury or 15,000 troops in a military emergency. She soon claimed the Atlantic speed record for a passenger vessel-three days and 10 minutes. Surely, went the conventional wisdom, few people would ever want to cross the ocean more swiftly.

Meanwhile, at the de Havilland factory in Britain, designers were fussing with plans for a commercial jet airliner...