Context: https://www.scribd.com/document/899239966/Henry-the-Green-Engine-1951-Scanned-by-ThatERTLGuy#page=64 page 60 of the book, 64 of the document.
Written version in case someone doesn't want to click on random links:
The Guard's flag waved, his whistle blew, and they were off. Soon in the distance they saw the bridge. There were the boys and they all had stones. "Are you ready, Henry?" said this Driver. "Sneeze hard when I tell you." "Now!" he said, and turned the handle. "Atisha Atisha Atishooooooh!" Smoke and steam and ashes spouted from his funnel. They went all over the bridge, and all over the boys who ran away as black as ####.