[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 the period of revolution is much slower. Position errors average out as certainly if not as frequently. In Bonniksen's "Karrusel" watch of 1893[2] the duration of a cycle is 52.5 minutes[3] while in the Auburndale Rotary which we are about to discuss the period of each revolution is 2-1/2 hours.
----- [1] Paul M. Chamberlain, _It's about time_, New York, 1947, p. 362.
[2] British patent 21421, granted January 21, 1893.
[3] Chamberlain, _op. cit._ (footnote 1), pp. 229, 230.
The patent model of Jason R. Hopkins' revolving watch, now in the U. S. National Museum,[4] was not the first in which the entire train revolved but it was a very novel conception intended to reduce greatly the number of parts usually associated with any watch. This may be seen from figures 2 and 3, where everything shown inside the ring gear revolves slowly as the main spring runs down. This spring is prevented from running down at its own speed by the train pinion seen in mesh with the ring gear. Through this pinion motion is imparted to the escape wheel and balance, where the rate of the watch is controlled. The balance, being planted at the center of revolution, travels around its own axis, as in the tourbillon, at the speed with which the entire train revolves around the barrel arbor. This arbor turns only during winding. No dial or dial gearing is shown in the patent or exists in the patent model. The patent merely says, casually, "By means of dial wheels the motion of the barrel may be communicated to hands and the time indicated in the usual manner." No fine finish or jeweling has been lavished on the model, the only jewels present being in the balance cock which was utilized as it came from its original watch with only minor modification to the shape of its foot. Apparently the balance wheel itself is also a relic of the same or a similar conventional watch. There is no jeweling in the escapement or on the other end of the balance staff. In spite of this the model runs very actively and will overbank if wound up very far. The beat of the escapement is two per second and the movement revolves once in 20 minutes.