It's easy to forget now, but the airship was once the Flying Machine of the Future.

In late 1929, Alfred Smith, the former governor of New York and the head of the group constructing the Empire State Building, announced an increase in the height of the planned edifice. Instead of the originally proposed 1,050 feet, the final building would scrape the sky at 1,250.

The extra height, it turned out, was meant to accommodate a mooring mast for dirigibles. A dock at the top of the Empire State Building, it was thought, would allow airships like the Graf Zeppelin to fly passengers directly to Midtown Manhattan -- where the vessels would "swing in the breeze" while those passengers walked an attached gangplank down to the street below. Airships, the "lighter-than-air aircraft" that were the first vehicles to enable controlled and powered human flight, were thought to represent the future of commercial aviation. And Smith wanted to ensure that his grand new building would be New York City's anchor to that future.

A quick scan of the current Manhattan skyline will reveal an Empire State Building towering above Fifth Avenue at a Zeppelin-friendly 1,250 feet ... its spire, however, lacking an attached airship. Not long after 1929, dirigibles and their fellow aerostats would fall out of favor as the preferred technology of passenger flight, relegated to the sports-recording and advertising purposes we tend to know blimps for today. The decline was due in part, to be sure, to a series of highly publicized accidents, including that of the Hindenburg, which burst into flames over Lakehurst, New Jersey 75 years ago this Sunday. But the quick niche-ification of the airship was due mostly to the fact that the gaseous materials that allowed dirigibles their effortlessness of flight -- hydrogen, plentiful but dangerous, and helium, safe but relatively rare -- ultimately proved less effective than the heady stuff that powers the airships of today: fossil fuels. Flight won out over float.

French postcard, 1910

Given how paradigmatic airplanes have become, though, it's easy to forget how similarly paradigmatic airships once were. If technology is a kind of Darwinian race, dirigibles and their counterparts spent a long time, actually, winning. In the 1930s, as the Empire State Building grew beam by beam and slab by slab, people awaited -- and expected -- a future that would find them voyaging and dining and sleeping and dancing in the sky.