Some interesting "Line Shaft" sites:

Before there were such names as Delta, Jet, Powermatic, Festool, Porter-Cable, etc., there was the line shaft.  Woodworkers in production were always in need of increasing productivity while reducing man-hours in order to remain competitive, and the solution came about the time the industrial age ducked it's tall head beneath the woodworker's cottage/shop door and entered.

The line shaft was a large overhead metal shaft that ran the length of the shop, initially powered by water where available and later by steam engine, the internal combustion engine, and even electricy.  The shaft spun in carefully placed bearings and was fitted with large-diameter pulleys similar to the PTO pulleys you've seen on the sides of, say, Farmall tractors.  Belts would run from the pulleys to the table saw, band saw, or whatever tool had been fitted.  Because the shafts ran continuously and powered many tools in the shop, individual tools were clutched in order to take them out of service.  Here are a few links for line shaft shop information.

Hanford Mills Museum (Meredith, NY)

A treatise on Pullies and Belting

An interview with Patrick Haire, who runs a line-shaft woodworking shop in Humbolt, Kansas.

Here's a Construction Today magazine article on the John Grass Woodturning Shop of Philadelphia, PA, a production turning shop once run with electric-powered line shafts.

Keith Rucker is involved in a project to help us recover understanding of Old Woodworking Machines.  This site is a gem if you are looking for information on line shaft driven Crescent Band Saws, or even that old Craftsman table saw that was your grandfather's.