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History
Henry Ellis Warren was born in 1872 in Boston USA and trained in electrical engineering at the Massachusetts Institute of Technology. He experimented with his early electric clocks in his own time while working in the Lombard Governor Company supervising work on their water wheel governor and inventing, among other things, water powered lathes. He set up his own company cutting gear wheels and subsequently, in 1912-14, the Warren Clock Company in Ashland Massachusetts. This made prototype clocks from 1914-15. When commercial production started in about 1915 the company moved in with the Lombard Governor Company.
Clocks and timekeeping products
This folder contains information on only the battery powered domestic mantle clocks by Warren, including the ‘mystery’ clocks. After 1916 when Henry Warren developed the synchronous motor, his attention turned to mains powered clocks (Telechron clocks), covered in different folders, and the master clocks required to maintain the mains frequency to drive them.
The earliest surviving clocks are half second pendulum clocks with a count wheel mechanically linking the electromagnetically driven pendulum to the movement through a ‘lift and drop’ count wheel. In this system a toggle on the pendulum lifts the count wheel, which rotates one tooth as drops back into place. These are very rare.
Later clocks from the main production look superficially similar but have two small horseshoe magnets mounted in a flat bar behind the pendulum rod just below the dial housing. As the pendulum moves, these turn a magnetic arm or flag connected to a worm drive inside an oil filled gearbox to turn the movement. A separate permanent magnet on the gearbox ensures appropriate polarity in the rotating flag. There is no mechanical linkage between the pendulum and movement and this is why the clock is referred to as a ‘mystery clock’. The pendulum is driven by a C-shaped magnet on the lower part of a pendulum attracted to a coil triggered by a mercury switch on the pendulum as it passes the vertical.
There are also developments recorded between these two types of clock, but these are extremely rare.
Patents
US patent 927,907, Electric Apparatus for Driving Clock or Similar Mechanisms, granted on July 13th, 1909. This describes an electromagnetically impulsed pendulum linked to a mechanical clock movement by a conventional pawl and count wheel. The coil is triggered by a mechanical switch. There are no known surviving clocks of this type.
US patent 1,089,886, Electric Apparatus for Driving Clocks or Similar Mechanisms of March 10th 1914 (filed Dec 1909) in which the C shaped magnet and flat coil are first seen, still activated by a mechanical electrical contact
US patent 1,144,973, Electric Apparatus for Driving Clock or Similar Mechanisms (filed July 1910) of June 29th 1915 introduced the mercury switch on the pendulum rod to trigger the electromagnet, called a pulsator by Warren. The patent drawing still shows coupling to the movement by a pawl and count wheel. The mercury switch is claimed to control the pendulum arc by varying the impulse duration.
US patent 1,160,346 Clock Mechanism (filed Nov 1914) of Nov 16th 1915 describes the final production clock with mercury contact and mystery magnetic linkage to the movement.
US patent 1,283,430 Apparatus for converting reciprocating motion into continuous rotary motion of 1915 expands on the mechanism of the magnetic linkage
Serial numbers
Serial numbers only appear on the main production run of the clocks with magnetic coupling to the movement. The serial numbers are written in ink in several places, usually on the movement mounting block, on the mounting post, back of pendulum and inside the base, but the ink is easily rubbed off and must be treated with care.
Clock markings
The main production clocks are marked with patents for 1909, 1914 and 1915 on the movement cover, have levelling feet and a rate adjuster on the base
Power supply
All these clocks run on 1.5 Volts. The original battery was very long and thin, but a C sized cell in a spacer tube can be used. The battery slides into the supporting pillar; take care not to bend the sliding arm that rotates over the top to make contact. Some makes of D cell fit the tube, just, but are dangerously tight.
Restoration and repairs
KEY TIPS TO AVOID DAMAGE – EASILY DONE:
Do not tip upside down, oil may leak from the gearbox, it is only closed with a cork in early models.
Never move with the pendulum in place, the coil is easily damaged by the ends of the magnet, even just when removing the pendulum
Do not try to unscrew the ends of the mercury switch housing, the switch will break as it is soldered to one end
Take great care not to inadvertently remove your clock’s serial number by cleaning (see above).
Domes are made of very thin glass
The clocks have a modular construction intended to make repair and moving the clock easy.
To check the mercury switch it is important to know that the contact is only closed when the pendulum is vertical, not tilted. Failure to impulse if the switch works may be due to loss of insulation in the circuit around the suspension. Current flows from the case to the suspension spring and then to the switch via the flat spring behind the pendulum rod. When the switch is closed it flows back up the pendulum rod to the battery via the hook and pin on the lower end of the suspension spring, which is insulated from the main spring and carries a connection back to the battery.
The coil resistance should be 60-65 ohms. Breaks in the coil are usually in the outer layers of the coil.
In a properly running clock the amplitude should bring the centre of the gap in the magnet past the centre of the coil. The amplitude can be adjusted by changing the angle of the mercury switch using a screw on the back of the pendulum but this is difficult to adjust and needs very fine tuning. The maximum amplitude possible without the pendulum hitting the coil is required. The magnets in the flat box on the pendulum rod must be as close as possible to the flag in the gearbox. If the clock runs backwards the magnets have been reversed.
The oil filled gearbox is difficult to clean. The worm must turn freely, under its own weight if the assembled gearbox is turned over in the hand. Opening and repairing this part is very difficult. The gearbox should contain 1ml light mineral oil such as Crystal Plus 70FG. Read Richard Hatch’s article on Clockdoc before attempting to repair the gearbox, or indeed any other component.
Practical tips
These clocks only run well when level and even then are not good timekeepers. Unless restored, few Warren clocks run when found.
Buying and selling
All Warren battery clocks are quite rare but come up at auction in the US, and less frequently now on Ebay.
Sources of information
The Keystone Weekly June 6th, 1916. No 8, the first description of the clock
“Modern Electric Clocks” by Henry E. Warren. A paper read at a meeting of the Clock Club held at the Old State House, Boston, on February 6, 1937. Aavailable on line at: http://clockhistory.com/telechron/company/documents/warren_1937/index.html
John M. Anderson, "Henry Warren and His Master Clocks," National Association of Watch and Clock Collectors Bulletin, 33 (August
1991): 375-395.
The “Mystery” of “The Warren Magnetic Clock”, the first Synchronous Motor Powered Clock? By R. Hatch, a definitive source of information available in the Warren folder on Clockdoc.
Last updated Feb 2020 author: Richard Hatch, California, richfhatch@hotmail.com
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