Most descriptions of the Mercury are vague and contradictory. However, it seems that the Mercury is somewhere between a keyboard typewriter and an index typewriter. The keys rotate the typewheel to the correct position, but do not bring it to the printing point. Printing is done by means of the large key at the left, which lifts the platen up to the typewheel! The typewheel is inked by the large ink roller to its right. The Mercury uses a three-bank QWERTY keyboard; the shift keys slide the typewheel along its axis. The typewheel's location on the right end of the typewriter is another very unusual feature. Some sources claim that this design made the printing more easily visible, but I don't see why it would.
Ernst Martin, in Die Schreibmaschine und ihre Entwicklungsgeschichte, claims that there was a second model of the Mercury on which the shifting could be done either by a small lever on the left side of the machine, or by a lever which was an extension of the axle of the typewheel.
According to Martin, the few specimens of the Mercury which sold, sold for eight guineas. They weighed only 8 lbs. (3.5 kg) and measured 7.5" x 7.5" x 4" (22 x 22 x 12 cm).
The drawing at the top of this page comes from Friedrich Müller's Schreibmaschinen und Schriften-Vervielfältigung (1900). Other drawings in typewriter books are based on this one. But it is unclear in this drawing where the space bar and shift keys are. I am not aware of any photographs of the Mercury.
The Mercury was not Myers' only invention, although it is the only one that was actually produced. His first invention was a circular-keyboard typewriter that is just as original as the Mercury. In this machine, as we can see from the 1886 patent drawings, the keys were attached directly to the typebars, which radiated outwards from the printing point, forming two semi-circles on either side of the platen. Myers also invented a four-bank typewheel typewriter before coming up with the Mercury.
I know of no Mercuries either in
museums or in private collections. So if you find one at the flea
someday, do pick it up!
Read more about the Mercury on Robert Messenger's site.