[Illustration: 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 factor, then we see that this will require 90 turns of the main spring, a manifest impossibility in view of the space available.[5] [Illustration: Figure 3.--ORIGINAL PATENT MODEL OF THE HOPKINS WATCH, U. S. Patent 161513, July 20, 1875, now in the U. S. National Museum (_cat. no._ 309025).] [Illustration: Figure 4.--DRAWING FROM U. S. PATENT 165831, showing Hopkins' first design improvement, an arbor for the barrel and train to turn on and the balance displaced from center.] Probably no attempt was made to produce a finished and practical watch at this time, although Hopkins, the inventor, was an actual watchmaker as well as a retail jeweler, with premises virtually in the shadow of the Patent Office. He was a native of Maine[6] and had been established in Washington since 1863, or perhaps some time in 1862.[7] [Illustration: Figure 5.--HOPKINS' BALANCE ARRESTING DEVICE, the subject of U. S. patent 165830. This and the device illustrated in figure 4 originally were submitted together to the Patent Office on June 9, 1875, and later were divided into two patents.] ----- [4] Cat. no. 309025; U. S. patent 161513, July 20, 1875.