To operate the Dart, one turns the knob on top until the selector points at one of 41 characters. This makes the central, vertically mounted typewheel revolve, brushing against an ink roller, until the desired character is pointing straight down. One then pushes the knob down in order to print, which also advances the machine one space forward. The Dart uses rubber type which prints capital letters. Simple, but ingenious.
The Dart pictured above, formerly owned by a friend of mine, is marked as follows on top:
It is usually said that the Dart was not patented until 1890. But this specimen is evidence that its inventor, L. Dart, obtained at least one patent in 1889. "Model: 1894" presumably refers to the year this model was introduced. Another model, probably earlier, has a simpler index/nameplate. The machine was advertised as late as 1904.
The Dart's dimensions are: typewheel diameter, 6 3/4"; character height, 1"; character width, 3/8". (The claim in some sources that the typewheel is 18" in diameter is incorrect.)
The Dart was useful enough that it was exported to Europe. Friedrich Müller's Schreibmaschinen (1900) illustrates and describes the machine in some detail. It was sold in Germany for 45 marks by Groyen and Richtmann of Cologne.
You never know where you may find an object like this. I hear that one was found serving as a doorstop in an antique shop. But don't use yours as a doorstop -- it's a valuable item.