Two days this summer have been unusually short, with the shortest expected on Aug. 5, leading global timekeepers to consider adding a negative leap second. The Earth's rotation has accelerated in recent decades, leading scientists to consider adding the first ever negative leap second. Earth is spinning so fast that global timekeepers are considering something that's never been done before: adding a negative leap second. So far this year, July 9 and July 22 have been unusually short — by about 1.3 and 1.4 milliseconds, respectively. However, Aug. 5 is expected to be even shorter, losing roughly 1.5 milliseconds, according...