Figure 2. — Patem Drawing of the Hopkins 

 Watch. Tlic 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 inodel 

 by riveting two ordinary springs together end to 

 end. Over this barrel and attached to the sta- 

 tionary frame of the watch is placed a large thin 

 ring A. cut on its inner diameter with 120 teeth. 

 Near its edge the barrel /s carries a stud g on which 

 runs a pinion of 10 in mesh with the ring gear A. 



the pinion and internal gear, and no adequate sup- 

 port 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. 



The second fault is in the ratio between the time cf 

 one revolution and the number of revolutions neces- 

 sary 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 safetv 



On this pinion is a wheel of 80 driving a pinion of 

 6 on the escape-wheel arbor. The 1 5-tooth escape 

 wheel locks on a spring detent and gives impulse 

 to the balance in one direction only, being a con- 

 ventional chronometer escapement. The inter- 

 mediate wheel and pinion, balance wheel, and 

 balance cock have been adapted from a Swiss 

 bar movement of the time. 



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). 



52 



BULLETIN 218: CONTRlBL'l IONS 1 R(JM 1111. .ML SEIM ()!■ HISIORV .AND TECHNOLOGY 



