It was 1:30 a.m. on Sunday, October 22, 1879, and experimenter Francis Jehl was still at work. He had been at his desk for ten hours, hunched over, carefully evacuating the air from a pear-shaped lightbulb. It wasn’t an unusual workday for him. His boss’s log routinely noted curious work habits: “we worked all night” or “32 continuous hrs.” or “60 hrs.” or “six days this week.”
In fact “the Old Man,” as “the boys” affectionately called their boss even before his hair turned gray, preferred to work at night when the...