The history of both traditional and electrical horology contains relatively few basic methods for controlling a timekeeper. The different types of oscillator and escapement are very well known and need not be described here. Suffice it to say that it is very seldom that a system that is fundamentally different makes its appearance. However, sometime in the late 1950s a remarkable clock was put on the market by Sessions which, as far as I'm aware, used a method of achieving an accurate timekeeper that had never been seen before. It was based on US patent 2,523,298 awarded in June 1950 to A. W. Haydon (a manufacturer of motors and motor controls) in which a 1.5 volt DC motor is directly controlled by a balance wheel.
Haydon's patent was not specifically aimed at horological applications but at the general area of governors for variable speed motors. Nevertheless, its potential for application to a new form of clock must have been obvious. It is not clear whether Sessions manufactured the clock using the patent or whether the movement was supplied complete by Haydon, but either way, confidence in the device was such that Sessions offered a specification that was described as revolutionary. In summary, it claimed to be a
“Million dollar patented governing device that automatically compensates for changes in battery voltage, motor load, and lubrication to keep running in perfect time all the time”.
On top of all that an unconditional lifetime guarantee was offered.
The clock was reviewed by the distinguished horologist Henry Fried in June 1959 who wrote:
“SESSIONS CLOCK CO. recently added a new and most interesting timepiece to the growing field of electrical horology. It is a battery-driven direct current motor clock with a chronometric governor. Simply stated, this is a clock in which a battery operates a small D.C. motor which drives a set of hands. The speed of the motor is governed by a balance and hairspring, the purpose of which is to permit or deny power to the motor in order to synchronize the motor’s speed (150 RPM). The balance makes the usual 300 beats a minute. In turn, the motor brush springs act as a constant force impulse to the pallet fork which impels the balance. There is no escape wheel; only a pallet fork and lever arm.
The clock measures approximately 1 3/4 x 2 1/2 inches and is powered by two pencil-type light batteries in parallel. The timekeeping qualities are unusually good. This is due to the constant force which impels the balance and controls the speed of the D. C. motor which drives the dial train. The balance has nothing to do but unlock the fork lever from its magnetic banking position. The action is fascinating to observe”.
In spite of these revolutionary claims, it seems that nothing is now known about this clock. What has become of it? Each clock was issued with an ownership number. I happen to have number 390 and can confirm that it is still working and keeps remarkable time. Yet I can find no one else who has even heard of it. How can such an extraordinary mechanism have disappeared? Perhaps it was too expensive to make in a competitive market, or was just too much of an oddball to catch on.
I have taken some macro images which will help to visualize the descriptions given and would add the following to Henry Fried's explanation. The balance wheel acts on a pivoted lever that instead of an anchor releasing an escape wheel, has a pallet that engages between the ends of the pair of commutator brush wires. The commutator itself is eccentric causing the long brush wires to 'wobble' and this keeps the balance oscillating. At the same time, the balance causes the lever to lift the brushes off the commutator thus interrupting the supply at the balance frequency.
Bill and I would be most grateful to learn of anyone who can add some light to this mystery. The existence of other examples would be great and anyone with a run of Sessions catalogues from 1959 to about 1965 could perhaps prove how long it was offered for sale and at what price.
David Read, London England. NAWCC member 0074055.