there formed the basis on which American watch making grew to such a
point that by the 1870's watches of domestic manufacture had captured
nearly all the home market and were reaching out and capturing foreign
markets as well. In spite of this great achievement there remained a
large untapped potential market for a watch which would combine the
virtues of close time keeping and a lower selling price. Only a radical
departure in design could achieve this. Rivalry between the several
existing companies had already produced an irreducible minimum price on
watches of conventional design.

The great obstacle to close rate in a modestly priced watch is the
balance wheel. This wheel requires careful adjustment for temperature
error and for poise. Of these two disturbing factors poise is the most
annoying to the owner because lack of it makes the watch a very erratic
timekeeper. A watch in which the parts are not poised is subject to a
different rate for every position it is placed in. This position error,
as it is called, can and often does cause a most erratic and
unpredictable rate. Abraham-Louis Breguet, the celebrated Swiss-French
horologist of Paris is credited with the invention, in 1801,[1] of his
tourbillon, a clever way to circumvent this error.

[Illustration: Figure 1.--BREGUET'S TOURBILLON. At C is shown the
carriage which revolves with pinion B carrying the escapement and balance
around the stationary wheel G. (After G. A. Baillie, _Watches, their
history, decoration, and mechanism_, London, Methuen, n.d.)]

His solution was to mount the escapement in a frame or "chariot" which
revolved, usually once a minute, so that with each revolution all
possible positions were passed through (fig. 1). This gave the watch an
average rate which was constant except for variations within the period
of revolution of the chariot. Only a very skillful workman could,
however, work with the delicacy necessary to produce such a mechanism.
The result was that few were made and these were so expensive that it
continued to be more practical to poise the parts in a conventional
movement. The idea of revolving the entire train of a watch, including
the escapement, seems to have evolved surprisingly slowly from Breguet's
basic invention of the revolving escapement. In constructing a watch
wherein the entire train revolves, no such delicate or precise
workmanship is required as in the tourbillon. Due to the longer train of
gears involved t