July 1874 saw the unveiling of three American technological advances that would have great importance in years to come. On July 4 the Eads Bridge in St. Louis was ceremonially inaugurated. The bridge consisted of three arches, each with a span of more than 500 feet, at a time when anything longer than 350 feet was thought to be unsafe. The controversial design worked because the arches were made of steel, which had just recently, with the introduction of the Bessemer process in the 186Os, become cheap enough to use in large quantities. Moreover, to anchor the bridge in the Mississippi’s muddy bottom, the designer, James Buchanan Eads, had sunk its piers all the way down to bedrock, 100 feet or more below the river’s swirling surface. As impressive as this accomplishment was, it had taken a heavy toll in lives.

The extra-deep piers had been excavated with caissons—sealed chambers with no floor, filled with compressed air, that sat on the riverbed as workers dug out the sand. As the caissons penetrated farther and farther below the surface, they required greater and greater air pressures inside. The technology was new to America, and dignitaries visiting the pressurized chambers laughed as they tried unsuccessfully to whistle or blow out candles. Workers were less amused when they started feeling intense pains in their limbs and joints upon returning to the surface.

The mysterious “caisson disease,” nowadays known as the bends, ended up killing fourteen workers and sending scores more to the hospital. By the time the digging ended, doctors had found that the disease could be mitigated by depressurizing slowly after workers left the chamber. Still, the ailment was poorly understood, and the physiological cause—nitrogen bubbles in the bloodstream, clogging capillaries—would not be appreciated for decades. Prevention and treatment remained a matter of trial and error. Over the next few years, despite the cautionary experience of the Eads Bridge, many workers on the Brooklyn Bridge (including its chief engineer, Washington A. Roebling) would be severely disabled by caisson disease.

On July 8 Thomas Edison successfully demonstrated his quadruplex telegraph, which allowed four messages to be sent along a single wire, two in each direction. The twenty-seven-year-old Edison had been working in telegraphy for more than a decade, as an operator and then as an inventor. He had come up with some useful improvements, enough to support himself and start a family, but he had lived hand to mouth for much of that time and was constantly borrowing money. The quadruplex was Edison’s first big score. He sold his rights to the financier Jay Gould for thirty thousand dollars, which he used to pay off debts, rent larger quarters for his business, and move his family from a small apartment over a drugstore to a house in a residential area. Tellingly, though, the first thing Edison did after receiving his payment was to splurge on several hundred dollars’ worth of