How long this period of development and experimentation required is unreported. It could hardly have started before early June of 1875, when application was made for the patent (165830) to prevent overbanking. The cash book of William B. Fowle of Auburndale, Massachusetts,[14] tells us that he bought half of William D. Colt's half-interest in the Hopkins rotary in March 1876, partly for cash but including a royalty on each watch made. Half this royalty was to go to Hopkins, a quarter to William D. Colt, and a quarter to William B. Fowle. Does patent 179019, issued June 20, 1876, to Hopkins, who assigned it on June 10, 1876, to Fowle,[15] represent the last improvement offered to Merritt? It covers a device actuated by a spur on a balance staff to lock the detent against tripping when in one position and to permit normal operation of the chronometer escapement when in the other position (see fig. 6). Another patent applied for on January 12, 1876, was in prospect and finally issued as no. 186838 on January 30, 1877, assigned to William B. Fowle on November 21, 1876.[16] This is much the most practical and useful patent in the series. A comparison of these (see figs. 7 and 8) with the Auburndale rotary watch (see fig. 9) shows a remarkable similarity between the inventor's conception and the product eventually manufactured. A practical center arbor to support and guide the entire rotating mechanism is here combined with a stem-winding and lever-setting mechanism and dial gearing in a well thought out arrangement. [Illustration: Figure 8.--REMAINING DRAWINGS FROM U. S. PATENT 186838, showing the dial gearing used in the Auburndale rotary.] Here, where the story of the Hopkins watch diverges from the interests who later brought out the rival Waterbury watch, it seems appropriate to call the reader's attention to the basic points of novelty and merit in the Hopkins watch which carried over to what became the Waterbury, somewhat as an hereditary characteristic passes from generation to generation. Previous writers have realized that one of these watches led to the other and have grouped them together because of the rotating feature which they shared in common. Beyond this point they have treated the watches as though they had nothing in common. Actually several basic features of the Hopkins watch existed in both: the long narrow spring in a barrel approximately filling one side of the watch case, a train rotating in the center of the watch and driven by a planetary pinion in mesh with a gear fixed to the stationary part of the watch, a slow beat escapement, and probably the hourly rotation of the train and escapement. When these details appeared in the first watches manufactured for Messrs. Locke and Merritt by the Benedict and Burnham Manufacturing Co. and later the Waterbury Watch Co., they were vastly changed in detail and much better adapted to mass production, although still basically the same.