standing. But it is almost impossibly difficult to calculate longitude if you can’t tell the time, in either Greenwich or the wilderness. Englishman John Harrison had invented a clock that was reliable and portable, making it possible to know both times. Captain James Cook had used the Harrison chronometer in the Pacific Ocean in 1775, proving its superiority. But the rigors of overland journeys were too much for such delicate instruments—they got banged around, they
