About Master Clocks

A master clock is the central timepiece in a time distribution system. Unlike an ordinary clock that simply displays the time, a master clock's purpose is to maintain the most accurate time possible and distribute that time to a network of secondary (slave) clocks. Before the era of quartz oscillators and atomic clocks, electromechanical master clocks were the backbone of accurate timekeeping in railroads, telegraph offices, factories, schools, and government buildings.

The clocks shown in this collection represent several of the most important American and British manufacturers of master clocks from the late nineteenth century through the mid-twentieth century. Each used a different approach to the fundamental challenge of keeping a pendulum swinging with minimal interference while simultaneously generating electrical impulses to drive remote clocks.

Stromberg

Stromberg master clocks used a spring-driven mechanism that rewound itself every minute. The brass and wood pendulums in these clocks are characteristic of early twentieth-century American master clock design. The deco-style model shown here represents a later evolution of the design, replacing brass hardware with chrome in keeping with the Art Deco aesthetic of the 1930s and 1940s.

E. Howard

The E. Howard Clock Company of Boston was one of America's premier clockmakers. Their master clocks featured mercury pendulums -- two glass jars of mercury that compensated for temperature changes by shifting the effective center of gravity of the pendulum. As temperature rose and the pendulum rod expanded downward, the mercury expanded upward, keeping the pendulum's period remarkably stable. The spring-rewind mechanism operated every minute.

IBM

IBM entered the time distribution business through its acquisition of the International Time Recording Company (ITR). Their master clocks ranged from weight-driven models with motor-wound weights to spring-driven movements. The deco and etched cases reflect the styling of different eras. The mercury pendulum models provided the highest accuracy, while the invar pendulum models used a nickel-iron alloy with an extremely low coefficient of thermal expansion.

Standard Electric

Standard Electric master clocks were common in commercial and institutional settings. The "eyebrow" case style -- named for its curved top -- is one of the most recognizable master clock designs. These clocks featured a pilot clock on the dial face and a program tape mechanism for scheduling bell signals and other timed events.

Self Winding Clock Company (SWCC)

The Self Winding Clock Company of New York was perhaps the most significant manufacturer in American time distribution. Founded in 1886, SWCC partnered with Western Union to create a nationwide time service. Their clocks contained self-winding mechanisms powered by batteries, eliminating the need for manual winding. The B-style and F-style movements represent different generations of their technology, with the F-style military model representing the highest grade of construction with its all-chrome invar pendulum.

Telechron

The Telechron master clock in this collection uses multiple synchronous motors locked to the 60 Hz power grid. Henry Ellis Warren, Telechron's founder, pioneered the use of synchronous motors for timekeeping and was instrumental in convincing power companies to maintain the accuracy of the 60 Hz frequency standard.

Synchronome

The Synchronome system, developed by Frank Hope-Jones in England, is one of the most elegant master clock designs ever created. The master pendulum swings freely for 30 seconds, receiving a tiny impulse every half-minute just sufficient to keep it going. This near-free pendulum design made Synchronome clocks among the most accurate pendulum timekeepers ever built, and they served as observatory standards well into the twentieth century.

For more information on the Self Winding Clock Company and the Western Union time service, visit ubr.com.