Maker, Warren Telechron, Inc., Ashland, Massachusetts, USA. Model Type E, c. early 1930's, serial no. 17.

Below are a few examples of electro-mechanical master clocks that were manufactured around the same time as the Telechron using a partial vacuum. The first picture is a very rare version by Clemens Reifler, Munich, Germany which is the only other fully glass enclosed master clock I know of. The second photo is the standard Reifler enclosure which is comprised of a copper tank with a glass 'bell jar' top. The bicycle looking pump is actually a hand vacuum pump. It is unknown how the Telechron's tank was evacuated whether by hand or machine operated pump.  The third photo is a master clock by William Shortt who worked with the firm of Synchronome, London, England. The wood cased clock, made by Synchronome, is the output for the master clock, which is enclosed in a similar type of copper tank as the Reifler.

The first photo below is a master clock by Mikhailovich Fedchenko which was the last electromechanical master clock to be made in 1970! Fedchenko's contribution to horology was his cycloidal pendulum which used his patented suspension spring that eliminated cycloidal error. Why would Russia go through the expense of making in the 1970's what was basically a 1930's technology when by this time the quartz controlled not to mention atomic clocks were well developed? One reason offered was that the Russians were afraid of their electronically-based clocks being wiped out in an atomic attack using a high altitude nuclear detonation to generate a high energy EMP (electro-magnetic pulse). The United States relied on heavy shielding. Lets hope we never find out if it works! Fedchenko's design still relied on a metal tank for its body, but did also have a bell jar at its bottom in addition to the top. This allowed one to use a beat plate and observe the pendulum directly from its tip. The last photo is my example by Earl Warren of Telechron. It differs in design from the others in that it is a floor standing model.