In Virginia Lee Burton's classic 1939 children's book "Mike Mulligan and his Steam Shovel," Mulligan often boasted that his steam shovel, Mary Anne, "could dig as much in a day as a hundred men could dig in a week, but he had never been quite sure that this was true." By the end of the story, Mulligan never gets the chance to prove his boast because electric, diesel and gasoline shovels have taken away nearly all of Mary Anne's work. Still, he finds an ingenious way for the old steam shovel to remain useful. When Burton wrote those words, she...