I've recently been reading some of the short stories of <a href="http://en.wikipedia.org/wiki/Dashiell_hammett">Dashiell Hammett</a> featuring the Continental Op.  These stories were written in the 1920s and are about a detective investigating crime in and around contemporary San Francisco.  

I noticed that the characters frequently use the word *machine* to mean an automobile, and I wondered whether this was common usage for the time and place.  I had not heard it before.  To a modern reader, it has an archaic sound, as if the car were such a new development that there was not yet a specific word for it.  But of course by the 1920s cars were very common, so this does not make sense.  It may also be slang; given their criminal associations, Hammett's characters tend to speak mostly in slang.

Does anyone have more information about this usage and its history?