Book excerpt: The portable steam engine is closely related to the traction engine but is not self-moving, requiring to be towed. It was designed to drive machinery such as threshing machines, saws and pumps. Less attention has been paid to portables than their industrial significance warrants and this book gives an overall picture of their history and development, dealing with portables at work and in preservation. Technical features are examined in some detail, especially where portable engine practice differed from that of tractions. The introduction of portable engines into agriculture was a major advance not readily appreciated in these days of diesel and electric power. Their use spread into the forestry, construction and manufacturing industries. Portables were still being made after traction engine building had ceased and the author describes some old working machines.