Driving wheels are generally larger than leading or trailing wheels . Since a conventional steam locomotive is directly driven, one of the few ways to ' gear ' a locomotive for a particular performance goal is to size the driving wheels appropriately.  Freight locomotives generally had driving wheels between 40 and 60 inches (1,016 and 1,524 mm) in diameter; dual-purpose locomotives generally between 60 and 70 inches (1,524 and 1,778 mm), and passenger locomotives between 70 and 100 inches (1,778 and 2,540 mm) or so. Some long wheelbase locomotives (four or more coupled axles) were equipped with blind drivers. These were driving wheels without the usual flanges , which allowed them to negotiate tighter curves without binding. 
At the age of thirty-one, Gilbert moved with her husband to the suburbs of New York and began trying to get pregnant, only to realize that she wanted neither a child nor a husband. Three years later, after a protracted divorce, she embarked on a yearlong trip of recovery, with three main stops: Rome, for pleasure (mostly gustatory, with a special emphasis on gelato); an ashram outside of Mumbai, for spiritual searching; and Bali, for "balancing." These destinations are all on the beaten track, but Gilbert's exuberance and her self-deprecating humor enliven the proceedings: recalling the first time she attempted to speak directly to God, she says, "It was all I could do to stop myself from saying, 'I've always been a big fan of your work.'"
Copyright © 2006 The New Yorker --This text refers to the Hardcover edition.