Читать книгу The Modern Clock. A Study of Time Keeping Mechanism; Its Construction, Regulation and Repair онлайн

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Wood expands .0004 of its length between 32° and 212° F. Steel expands .0011 of its length between 32° and 212° F. Lead expands .0028 of its length between 32° and 212° F. Brass expands .0020 of its length between 32° and 212° F. Zinc expands .0028 of its length between 32° and 212° F. Tin expands .0021 of its length between 32° and 212° F. Antimony expands .0011 of its length between 32° and 212° F. Total length of pendulum to adjusting nut 46 inches. Total length of steel to adjusting nut 2 inches. Total length of wood to adjusting nut 44 inches. .0011 × 2= .0022 inch, expansion of our steel. .0004 × 44 = .0176 inch, expansion of our wood. .0198 total expansion of rod.

We have 7 inches as half the diameter of our bob .0198÷7=.0028, ²⁄₇, which we find from our tables is very close to the expansion of zinc, so we will make the bob of that metal. Now let us check back; the upward expansion of 7 inches of zinc equals .0028×7=.0196 inch, as against .0198 inch downward expansion of the rod. This gives us a total difference of .0002 inch between 32° and 212° or a range of 180° F. This is a difference of .0001 inch for 90° of temperature and is closer than most pendulums ever get.