Segundo de Chomón probably didn't realize what a difference he'd made when, in 1907, he invented the camera dolly. In fact, it would be another seven years before the first tracking shot was used in a popular movie. Putting the camera on wheels seems like a no-brainer now, but for more than a decade in filmmaking's early years the camera was stuck in one spot. The camera dolly you'd find on today's movie set is much like the early dollies, heavy and stable. But today you'll likely find one of two manufacturer's names on the side -- J.L. Fisher or Chapman/Leonard.
The key to making smooth shots is the weight of the unit and the surface that the dolly rides on. Many smooth, hard concrete surfaces can be used with the dolly alone, but most of the time a track made from round metal tubes, much like a railroad track, is necessary to get the smooth tracking shots we're all used to. Modern dollies are essentially heavy sleds on four wheels that can move in any direction, with a hydraulic lift system for the camera. The cameraman rides on a seat attached to the dolly, and the whole unit is pushed with great accuracy by a dolly grip. Next time you see a movie shot of a couple walking down the street, just think of all the metal track laid on the ground beside them.