His solution was to mount the escapement in a frame or “chariot” which revolved, usually once a 51 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.
The Invention
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.
There are two great faults in the model. First is the lack of an adequate bearing for the barrel to turn on. There is only one very short bearing a long way removed from the point of engagement between 52 the pinion and internal gear, and no adequate support is given the barrel, with the result that it tends to deflect from the ideal or true position and to bind. This condition is aggravated by the fact that the ring gear was made by cutting its teeth on an angle to the axis around which it is to revolve, using only a saw of appropriate width. The teeth were then rounded-up to form by hand in a separate operation which by its very nature means that the teeth are not exactly alike. This lack of uniformity of the ring gear coupled with an entirely inadequate bearing for the barrel contributes to rather erratic transfer of power. These irregular teeth would not, of course, be a factor in factory-made watches where suitable machinery would be available for the work.
Figure 2.—Patent Drawing of the Hopkins Watch. The mainspring barrel E, of a very large diameter in proportion to the diameter of the watch, occupies nearly the full diameter of the movement. The spring itself, narrower and much longer than usual, is made in the patent model by riveting two ordinary springs together end to end. Over this barrel and attached to the stationary frame of the watch is placed a large thin ring A, cut on its inner diameter with 120 teeth. Near its edge the barrel E carries a stud g on which runs a pinion of 10 in mesh with the ring gear A. On this pinion is a wheel of 80 driving a pinion of 6 on the escape-wheel arbor. The 15-tooth escape wheel locks on a spring detent and gives impulse to the balance in one direction only, being a conventional chronometer escapement. The intermediate wheel and pinion, balance wheel, and balance cock have been adapted from a Swiss bar movement of the time.
The second fault is in the ratio between the time of one revolution and the number of revolutions necessary for a day’s run. Three turns of the spring are, of course, required to run the watch for an hour, since the barrel and train revolve three times in that length of time. If we choose to have the watch run for 30 hours on a winding, and this leaves but a small safety 53 factor, then we see that this will require 90 turns of the main spring, a manifest impossibility in view of the space available.[5]