National Geographic : 1919 Nov
MTINTKI CALLT BUILT WAITCE B~A^^ WAffT wr The Riverside The most dependable moderate price watch in the world $80 and up Know "the Works" of the HEWatch You Buy HE hairspring upon the balance wheel of a watch is similar in function to the Effect of gravity upon a pendulum in a clock. A pendulum swings so far to the left or right and is stopped and swung back to the point of impulse by gravity. A hairspring retards the balance wheel of a watch and re volves it back to the point of impulse, which impulse is given by the escapement. Therefore, as the hairspring controls the speed and arc of vibration of the balance, or its resultant, time, it is of the utmost importance to the time-keeping quality of the move ment that the balance and hairspring be mated in perfect ratio as to the weight of the balance and the proper rela tion of that weight to the center of gravity and the strength of the spring. To determine this absolute ratio, John Logan, a famous Waltham ho rologist, invented a vibratory machine (illustrated above) which so accu rately mates the Waltham balance wheel and the hairspring, so perfectly selects the right hairspring for the particular balance wheel, that when finally assembled in the watch the watch is a natural time-keeper. This is one reason why the Waltham watch is famous for its close and con stant time-rate. The foreign watch balance and hairspring are of varying construction. They are made by hand-one at a time-therefore it is impossible even for a skilled watchmaker to determine the ratio weight of the balance to the strength of the hairspring. Its determination is by the uncertain rule of thumb method in trying va rious hairsprings until one is found which approximately performs its function. This is yet another reason why the Waltham watch, due to standardized exclusive machinery, standardized material, absolute measurements and known ratios, is the watch you should insist upon buying And why the world's leading horologists came to Waltham for time. This story is continued in a beautiful booklet in which you will find a liberalwatch education. Sent free uson request. Waltham Watch Company, Waltham, Mass. WALTHAM THE WORLD'S WATCH OVER TIME "Mention The Geographic-It identifies you"