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Electric Clocks

Horloges électriques - Elektrische Grossuhren

By Michel Viredaz – Photos by Heidi Viredaz-Bader

English version revised by David Read

The following text is a revised version of a French article published in Chronométrophilia No 51 (publication of the Swiss Association for the History of Time Measurement: see www.chronometrophilia.ch).

This text contains eight animations made by J.E. Bosschieter (see after Fig. 5, 12, 13 (2x), 19, 20, 23 and 25). The first time you want to see an animation, you may have to download "Macromedia Shockwave ®". Then, loading the animation takes about 20-30 seconds. Use your browser's "Back" button to return to the text. If you like these animations, you can order a CD with 100 animated clocks to boscoclocks@zonnet.nl.

It should be explained at the beginning that this small paper is concerned exclusively with clocks, and not electric or electronic watches, which represent a totally different subject. The clocks discussed below are powered directly or indirectly by electricity and our historical description finishes with the arrival of electronics, which we define here as the introduction of semi-conductors in an electric circuit. In other words, we will cover approximately the period 1840-1970.

A second preliminary remark is necessary: the paper is aimed at amateurs of clocks in general who often know little or nothing about electric clocks. Such clocks are only known well by a small circle of enthusiasts despite their enormous interest and the fact - as we will discover - that they are much more varied in their principles than clocks that are purely mechanical.

Finally, but modestly and only for a better understanding of the text, we would like to make it clear that we are looking at the subject from a Swiss point of view, which may explain the choice of examples and emphasis in the text.

We will look in turn at following chapters or themes:

· classification,

· history,

· examination of the different principles, with examples,

· sources of documentation.

Classification of electric clocks

It may appear a little off-putting, but classification is a necessary approach if we want to have a clear overview of such a complex subject. The first example of systematic classification we find is the one of Swiss patents found in Inventions-Revue of 1908-1909. It is interesting in that it shows the spirit of the time but nevertheless insufficient for a retrospective examination of the subject. After class A devoted to mechanical horology, class B to cases and class C to specialised machines and tools, there are no less than 4 (!) classes for electric horology:

· Class D: Electro-magnetic independent clocks, divided between "direct action" and "indirect action".

· Class E: Systems for the unification of time by electricity (with 5 subsections).

· Class F: Electric apparatus for the measurement of fractions of the second (to make a special class of these rare but wonderful machines - like the chronoscope - was a real honour for Messrs Hipp and Favarger!).

· Class G: Electric mechanisms for giving time-signals.

For our purpose we prefer to use a more detailed classification based on three sorts of criteria:

· A functional classification:

o independent clocks (self-contained instruments giving the time at a given place),

o master-clocks (clocks with a system of electrical contacts to enable the transmission of time-impulses to more or less distant secondary clocks),

o secondary clocks (those instruments receiving the above-mentioned impulses),

o synchronous clocks (which are in fact nothing but secondary clocks which master clock is the generating station).

· A classification by type of movement (which can apply to both independent and master-clocks):

o clocks driven by electro-magnetic impulses to the pendulum,

o mechanical clocks with weight or mainspring rewound by electricity (through a motor or an electro-magnet, at short intervals or with power reserve),

o clocks in which a mechanical impulse is applied directly to the pendulum (through gravity, spring or electro-magnet),

o special and anecdotal ideas of construction.

· Finally a classification according to the source and characteristic of the electrical supply:

o low voltage (1.5-60V) or mains (110-220V),

o direct current (usually low voltage) or alternating current (usually mains),

o mains (with or without transformer and/or rectifier) or battery (rechargeable or not).

With such a global overview, it will now be easier in the following chapters to examine characteristic constructions, without the risk of confusion between the many varieties of electric clock.

But before that, let's have a look at history.

History

The first question that comes to the mind of everyone is "who is the inventor of the electric clock?" As usual for great inventions, the idea was everywhere in the air around 1840, and numerous works had been undertaken by people like Wheatstone, Steinheil, Hipp, Breguet, Garnier and many others.

Under the initiative of British enthusiasts, who pay more attention to electric clocks than other nationalities such as the Swiss or French, the idea has become well established in literature that Alexander Bain is the "father" of electric clocks. Bain started, but did not finish, an apprenticeship as clockmaker, and became interested in electricity at a very early stage of his life (around 1830). After a long controversy with Prof. Wheatstone, who tried to appropriate his invention for himself, he registered his first patent on the 10^th of October 1840. Bain is certainly a genius and a visionary. Numerous applications of electricity to clock making and time are envisaged in his texts and patents, but he did not succeed in establishing a real production series or an industry, as did Hipp (who was of German origin) in Switzerland at the same period.

But before we speak a little more about Hipp, let's spend a few words reminding ourselves that research on electricity had already started in the 17^th century. An Italian, Prof. Rami, made the first electro-static clock in 1815. William Sturgeon, a British citizen, invented the electro-magnet (indispensable for electric clocks) in 1825, and Volta the battery in 1800.

Matthäus Hipp (1815-1893), so important for the Swiss industry and today's collectors, was born in the Wurtemberg. He was apprenticed as a clockmaker and worked in a modern factory, where he met the son of the owner coming back from further training in Switzerland. He also decided to go to the French-speaking part of Switzerland to improve his professional education, stopping briefly in Sankt-Gallen in 1834. He arrived in Saint-Aubin near Neuchâtel in 1835, where he improved his skills for a few years, before returning to Germany. In 1841, 28 years old, he opened his own workshop in Reutlingen Germany. It is in Reutlingen that he finalized his first clock with the Hipp-toggle, presented in Berlin at an exhibition in 1843. It was however still a mechanical clock. It is most probably not before 1860 that he applied his system to an electro-magnetic clcok (Fig. 1). He also invented a small motor and built the chronoscope and the registering chronograph, two instruments for the measurement of very short time periods (the class F mentioned above...).

Fig. 1: General schema of a Hipp clock with 1/2s pendulum of the second half 19^th century. One can see the contact in the middle of the pendulum and the electro-magnet below it. These clocks exist with or without the master clock function.

The most remarkable fact connected with the Hipp-toggle clock (apart from its extraordinary ingenuity) is the fact that it was so good in practice that it could be made and sold for over hundred years without any change in its principle. What other invention can claim the same longevity? In 1852, Hipp was named by the Federal Government as Head of the National Telegraph Workshop and Technical Manager of the Telegraph Administration, a great honour for a foreigner. In this position he continued his inventions during eight years, but not without creating some animosity against him since he was both well known and his office was making profit, two major crimes for a high civil servant... G.A. Hasler, his former assistant, succeeded him and took over the workshop some time later, when it was privatised.

In 1860 Hipp went to Neuchâtel, where he created a telegraph and electrical apparatus factory. This was the real beginning of industrial electric horology, after two decades of laboratory research around Europe. The company developed rapidly and Hipp retired in 1889, leaving the responsibility to engineers A. Favarger and A. de Peyer. From this time until 1908 pieces are signed "Peyer & Favarger, successors of M. Hipp", after which Peyer retired and the company became the "commandite" (a system of company financing) Favarger & Cie (& Co.), then Favarger & Cie S.A. (Ltd.) in 1923 and Favag S.A. in 1927, date of the alliance with Hasler, which becomes Ascom in 1983-4 when they merge with Autophon. Ascom-Favag is finally sold to its competitor Bosshard (Moser-Baer) in 1989 and production stopped. Since 2002, Bosshard is named Mobatime. A portrait of Hipp can be seen on http://vlp.mpiwg-berlin.mpg.de/people/data/per328.html.

Another important person to name in the Swiss landscape of electric horology is David Perret, a pioneer of electric winding. He was the son of an industrialist in the watch business, high-school mechanical engineer from the Swiss Polytechnic Institute of Zurich, officer in the army and politician. He registered many patents in his name. After having spent some years concentrating on the mechanisation of watch production, he became interested in electric clocks and developed an original system of double contact switching (to reduce sparking) for rewinding a weak mainspring once a minute. He died on September 18, 1908, and sadly his company was liquidated some years later.

To end this small historical chapter, let's mention a few other important dates:

· 1856: the first electrically wound clock by Louis-F. Breguet,

· 1862-64: the first electric networks for clocks in Geneva and Neuchâtel,

· 1885: the invention of the Ferraris motor (much used in electrically wound clocks, for example Zenith),

· 1912: the first radio time-signals from the Eiffel Tower,

· 1916: the synchronous clock by Warren,

· 1921: the Shortt clock (the top of precision before quartz),

· 1930: the first quartz clocks,

· 1955: the atomic clock,

· 60s and 70s: the move from "electric" to "electronic" and end of our little review.

We can now go to the study of the different types of electric clocks.

Electro-magnetic impulse to the pendulum

This idea first appears, although in a rather primitive form, in the first patent of A. Bain in 1841. We find it also in the Hipp clock of 1842. In these clocks, an electro-magnet (i.e. a coil with a central core of soft iron) is placed generally below the pendulum, which is also terminated by a piece of iron. An appropriately positioned contact (this is easier to say than to do...) switches the current through the coil during the descending period of the pendulum, close to the vertical, giving it a magnetic impulse to replace the lost energy (Fig. 2 and 3).

Fig. 2: One second pendulum clock of the Hipp type signed Favarger & Cie, about 1910. The dial is an oscillation meter linked to the pendulum by a fork and a gathering system.

Fig. 3: Detail of the electro-magnet below the pendulum of a Favag 2/3s clock.

One realises that the pendulum is therefore both the regulating oscillator, as in mechanical clocks, but also serves as the clock's motor. The pendulum and its contact can work alone, without any wheels. The transfer of time to the dial can be done in two ways, either mechanically with an index wheel and a pawl, the movement being then just an impulsion-meter (a very simple system, not needing to be described to clock making specialists), or through an electric contact giving impulses to a secondary clock (see the "secondary clocks" chapter). This second solution has the advantage of leaving the pendulum almost free. It is used generally in high quality clocks (e.g. all Favag clocks with 2/3s pendulum).

Féry, in France, modified the electro-magnetic motor system by using a fixed impulse coil without a core, through which a permanent magnet attached to the pendulum oscillates. This system has been widely used in France by Brillié, ATO and many others. The same principle is used by the Bulle-Clock that employs, by contrast, a coil fixed to the pendulum and a magnet fixed on the movement or baseboard (Fig. 4 et 4bis).

Fig. 4: Bulle-Clock of the first period, around 1920, still signed MFB (for Maurice Favre-Bulle), who developed it. One realises that the trademark comes from his name (he was French but Favre-Bulle is a typical name from the Swiss Jura) and has nothing to do with bulls. The coil attached to the pendulum and the permanent magnetic bar fixed to the case are clearly visible. The contact is made by a silver pin carried on the pendulum rod that engages a pivoted notch on rear of the movement. The company lasted until 1955, when its founder died.

Fig. 4bis: Brillié second pendulum clock

A critical characteristic of these clocks is the contact that switches on the current needed to maintain the pendulum in oscillation. In most clocks of this type, the contact closes and impulse is given at every oscillation (or half-oscillation as with Frank Holden), and a pawl fixed to the pendulum drives the wheel train. The genius of Hipp was to invent a system of toggle switch that makes an electrical contact only when the amplitude of the pendulum falls below a critical threshold, thus freeing the pendulum from a lot of unnecessary mechanical interference (Fig. 5).

Fig. 5: The Hipp toggle contact. On the left, the general scheme, on the right, how it works. As long as the pendulum amplitude is sufficient, the pallet slides from side to side over the notched jewel; however, when the amplitude falls to a certain threshold the pallet engages the notch and lifts the contact spring. At this moment electricity flows through the coil and gives an impulse to the pendulum, sufficient for the next 30-120 vibrations.

Hipp clock animation.

In practice, impulse is given every 30 to 120s, depending on the model. As already mentioned, this system as been perpetuated in Hipp-Favag for about a century, and copied many times with all sorts of variations (English Magneta, Siemens, Cyma, Scott, Vaucanson, etc.).

Until now, we have been speaking only of pendulum clocks. However, smaller clocks and watches with a spiral-balance have been made on the same principles, as is the case in Switzerland and Germany, e.g. the well-known and more recent movements named Orel and Sterling. In this category, we can also mention the Eureka and some others like Cauderay - an electrician from Lausanne in Switzerland, who became established in Paris - who used a very large and decorative balance (Fig. 6).

Fig. 6: Cauderay's clock movement, end of 19^th century. The electro-magnet acts on a mass fixed to the pendulum shaft; the contact is derived from the Hipp toggle.

Finally, we note that the development of timekeepers based on the principle of magnetic impulse accelerated when the transistor replaced the electro-mechanical contact and it is in this category that the electronic revolution was started (ATO and Kundo).

Electric winding

The clocks described in this section are mechanical clocks of any type, with pendulum or balance, weight or mainspring, in which the winding is done electrically instead of manually. Some systems also exist for the later modification of a mechanical clock.

The winding can be done either with an electric motor (which winds many turns of the weight or mainspring at each contact) (Fig. 7) or with an electro-magnet and armature which winds small portions through a pawl, but the final result is the same (Fig. 8).

Fig. 7: Bürk clock from the Black Forest, around 1960. A small motor, switched by a mercury contact, does the winding.

Fig. 8: An EZ clock of the 1930s (EZ = Elektro-Zeit, later becoming T&N = Telefonbau & Normalzeit). In contrast to the common pawl and ratchet rewind system found in many electrically rewound clocks, the electro-magnetic system in the EZ system is composed of a two pole armature which is pivoted to rotate through about 25° into alignment with the magnetic field when the contact is closed, and returns to its resting position under the force of a weak spring when the contact is opened. This sudden rotational energy is transferred through the surface of the contact to a large flywheel that winds up a small weight, sufficient for driving the anchor escapement and pendulum for a few minutes until the process is repeated. This electro-magnetic "motor rewind unit", is a discreet module from which the pendulum also hangs, and the conventional anchor movement comprises another easily removable module (not in the picture) which counts the pendulum beats and displays the time on a dial. These two units are linked together by a helical spring through which energy is transferred with maintaining power. The clock illustrated has, in addition, two wheel trains linked by a differential, one for the time and one for the secondary clocks contact, revolving once per minute of a half-rotation and reversing the polarity at the same time.

Some clocks are wound at frequent intervals (once a minute as with David Perret) or at long intervals as in tower clocks. Some pieces have a power reserve; others can only go the period between two windings (for example the small Reform movement, made in large quantities) (Fig. 9).

Fig. 9: Small Swiss travel clock signed Cosmos, using the cheap version of the Reform movement, based on patents in 1928 and 1929. It has a spiral balance with a spring giving a power reserve of some three minutes to the going train. When the spring reserve is almost exhausted, a small arm linked to the barrel closes the contact and the electro-magnet gives a kick to an inertia arm with two balls at the ends. This winds up the spring with a pawl and ratchet and at the same time interrupts the contact. This movement is more commonly found in its high quality version, with 15 jewels and Breguet hairspring.

The power reserve is obtained by a weight or a spring, kept more or less fully wound through frequent switching, but which can go for the whole length of the spring or weight suspension during a power outage, the complete winding being made automatically when power reappears. In this category of clock, there is a need for a system that switches on or stops the winding at the right moment. In Moser-Baer and many other clocks, which use a powerful motor driving the rewind via reduction gearing, this is obtained with a contact linked to a sliding screw fixed to the going barrel. In some weight-driven clocks, the contact is switched by the weight itself when it goes up and down. In Zenith clocks, and others using a weak motor like the Ferraris (the one seen in most electricity-meters), the current is not interrupted as it is unnecessary for just 2W, but the wheel is stopped by a lever covered with felt, constructed on the same principle as above. The result is an almost continuous winding in small sequences of 2-3s. The motor only goes for a long period after a current interruption (Fig. 10 and 11).

Fig. 10: Wall clock with Ferramo balance movement, made by T. Baeurle & Sons, Sankt Georgen, Black Forest, using a Ferraris motor for the winding power. The main advantage of this motor is that it is silent, a quality which not all electric clocks can claim to have!

Fig. 11: Precision clock with heavy pendulum beating seconds from the Zenith company. The movement is weight-driven. The winding module is separate, based on a Ferraris motor, and placed below the movement. It starts as soon as the weight falls down by only a few millimetres, assuring a permanent power reserve of many hours. The movement is conventional, but of top quality with a jewelled Graham anchor. The same clock also exists in a manual version.

A very particular and rare case is the O'Keenan clock made in Paris, in which the motor turns continuously, its speed being regulated by the escapement itself through a buffer-spring so that it continuously gives just the necessary energy to the clock (Fig. 12).

Fig. 12: Clock made by O'Keenan in Paris, around 1905. It has a distinctive small motor known under the "OK" name and widely used in gas meters. It turns permanently, winding a buffer spring, which in turn gears a conventional movement. The escapement maintains the motor at a speed such that it never needs to stop.

Of course, in all these pieces, winding must be designed in such a way that it does not interrupt power to the escapement during the winding period, but this is a classic problem, well known in horology, especially in precision or large clocks. Concerning large clocks, let's mention the winding through a continuous Huyghens chain, often used to electrify old movements. Also, by adding a magnetic synchronisation of the pendulum through a radio-controlled clock, antique tower movements can be modernised without any non-reversible modification, a very important concept in restoration.

Wagner clock animation.

This animation represents a clock made by C.-T. Wagner of Germany. The clock is driven by two weights, one for the going train, one for the contacts, rewound every minute of the exact height by an oscillating electro-magnet in "Z" shape. A more detailed description is available separately.

Direct mechanical impulse to the pendulum

Included in this class are all clocks in which the oscillation of the pendulum is maintained by a mechanical (as distinct from electro-magnetic) impulse given directly to it, excluding of course the mechanical impulse through an escapement, as in mechanical horology. In more popular terms, we could speak of clocks receiving a flick from time to time! British clock makers are the kings of this technology, with numerous high quality examples (e.g. Synchronome/Shortt, ECS/STC, Gent/Pulsynetic, Gillett and Johnston, Telephone Rentals/Princeps). Continental clocks made on the same principle are somewhat less well known.

Before we examine some of them, we should mention that the impulse may be given in three different ways:

· by gravity (with electro-magnetic re-cocking of a gravity arm). This is the best solution, giving a constant power (Synchronome, etc.),

· by a spring, tensioned in advance by an electro-magnet and released by a count wheel. (Froment may well have used both gravity and spring but this is not clear from existing literature),

· by a lever moved directly by an electro-magnet.

In the first group, the stereotype is of course the Synchronome by F. Hope-Jones (Fig. 13), a wonderfully simple clock giving excellent chronometric results with a minimum amount of mechanics (one single wheel).

Fig. 13: Classic Synchronome clock of the 1940s, made with little modification since beginning of the century. Clearly visible is the single wheel which is gathered by a small jewelled arm fixed to the pendulum, as well as the gravity arm and the pallet on which it falls, before being kicked up again by the electro-magnet. A non polarised secondary movement is in the door and serves as main dial. Many other slaves can be placed in series on the same circuit.

Hope-Jones' Synchronome clock animation.

In this clock, the pendulum carries a lever with a gathering jewel that indexes the single 15-tooth wheel one tooth at a time. Once in every revolution (every 30s) the wheel releases a gravity arm that falls onto a pallet attached to the pendulum rod, giving it the necessary energy at the best moment. At the end of its downward movement the gravity arm touches an electrical contact on the armature of the electro magnet, and is thereby brought back to its upper position. One or more secondary dial clocks impulsed every 30s (including the main one on the door of the Synchronome itself), may by placed in the same switching circuit.

The Shortt clock derives from the Synchronome and was the highest precision clock before the arrival of quartz oscillators. It is composed of two clocks, a master under vacuum with an almost free pendulum, and a synchronised slave, which carries all the necessary devices and absorbs all interferences without influence on the precision of the master.

Shortt's clock animation

In the second category, we would like to mention the German made clock W. Zeh (Pega), an attempt in 1928 to design a precision clock for the public at large with the possibility to drive one or two secondary clocks for use in the home, however using a short pendulum (Fig. 14). An arm made of a flat spring is tensioned by an electro-magnet, which also drives the minute-wheel. The spring is released periodically to give an impulse to the pendulum through a needle leaning on an arm fixed to the pendulum and bearing a jewel. Criticism of this system was made, however, because of expansion of the needle that reduced the expected precision of the clock.

Fig. 14: Rear view of the movement made around 1928 by W. Zeh of Freiburg in Breisgau, here placed on a Bergeon support for the photography. One can see the lever made of a spring blade, and the needle pressing on an arm fixed to the pendulum. The electro-magnet is inside the movement and cannot be seen here. It advances the wheel train at the same time as it tightens the spring.

In the third category, we can place at least two great names: Professor Aron (who is better known for his later winding system used by the Heliowatt company), and Campiche of Geneva, whose clocks are highly valued by collectors. In Aron's patent of 1884 an electro-magnet moving an armature, gives impulse to the pendulum rod through a fork, which at the same time moves the minute wheel with a gathering pallet. The movement is, again, just an impulse-meter (Fig. 15).

Fig. 15: Aron movement of 1884, signed G. Becker, Freiburg in Schlesien. The electro-magnet is on the left and acts on the pendulum through an arm when the contact closes. The arm is linked to the pendulum and carries a pawl in order to index the wheel train. Interestingly, the dial has a minute sub-dial graduated in number of vibrations (80) and not seconds.

In Campiche's clock - another single wheel clock - the electro-magnet gives a flick to the pendulum rod once a minute through an elastic lever. A pawl on the pendulum indexes a 30-tooth count wheel carrying a seconds hand and making one turn per minute. It also carries a contact blade that closes the switch between two contacts, thus providing the necessary electrical contact for both the electro-magnet and for the circuit of secondary clocks, of which one serves as a secondary dial on the door of the case as usual (Fig. 16).

Fig. 16: Campiche.

The advantage of all these clocks is their great simplicity, and simplicity means minimization of interferences and hence, in principle, improved precision and less maintenance.

Secondary clocks

Secondary clocks are not self-contained clocks, but slave instruments that receive the impulses given by a master clock, and add them to display minutes and hours on a dial. They could never give the time by themselves and numerous amateurs who did not know this have made quite bad deals on flea markets! They need a master clock, which generally give impulses every 1s (high precision clocks), 30s (typically in France and the UK) or 1 minute (Germany and Switzerland) (Fig. 17, 18 and 19).

Fig. 17: Secondary clock by M. Hipp. Its armature is polarised and rocks from side to side in response to alternating polarity pulses transmitted from the master clock. The wheel train is indexed by driving a verge-like wheel and pallets in reverse. The motion work and dials exist in minutes and seconds versions, in different sizes according to the length of the hands.

Fig. 18: Secondary clock by A. Favarger, successor of Hipp. It has a polarised rotating armature and has been produced for about three quarters of a century in three sizes.

Fig. 19: Secondary clock by Favarger, medium size model.

Favarger secondary clock animation.

The master clock function is independent of the type of slave clock and all classes described above can play this role given the necessary contacts. Even a purely mechanical clock can act as in the master's role if fitted with appropriate contacts and many precision clocks have been manufactured on this basis.

It needs to be remembered that the motion work (counting system) of a secondary clock must suit the time interval between transmission of impulses, i.e. whether they are 1s, 30s or 1 minute. In addition, secondary clocks are made to suit both unipolar and reversing polarity pulses to match the system employed in the mother clock.

Therefore, apart from the impulse-frequency, secondary clocks can be divided into two large families: polarised and not polarised. Polarised clocks, used mainly in Germany, France and Switzerland, need alternate positive and negative impulses (usually low voltage) (Fig. 20).

Fig. 20: Polarity inversion device by Heliowatt. Every minute, a cam seen on the left makes a half-turn, closing the contact alternatively on each side, thus reversing the polarity.

Animation of a polarity inversion device.

This animation shows the system made by Badier and Paulin of Grenoble in 1888, quite similar to those of Hipp and Aron (Heliowatt).

The idea is to avoid involuntary jumps of the hands due to a vibrating contact or outside interferences. This means a special inverter device in the master-clock, obviously not a simple construction. Non-polarised clocks always receive the impulse in the same current direction. This means simplicity, but requires a well-designed contact. These clocks were usual in Great Britain but less so elsewhere. Nevertheless, they could be found generally, but in small numbers, at the beginning of electric horology (e.g. Campiche around 1900).

Constructional details are very varied and more or less noisy, but most if not all of them use an electro-magnet, a system of pawls or rocking pallets and a traditional wheel train.

The clocks of the Swiss Federal Railways made by Favag deserve a special mention. They have a seconds hand which stops for about 2s in every minute. In fact, for reasons of simplification and probably cost, they are an attempt to make secondary clocks with a seconds hand driven by mother clocks having only minute impulses. There are in fact two different types of movement arranged co-axially in these clocks: a normal minutes secondary clock, and a synchronous movement for the seconds hands, which is stopped during each revolution at 58s, and is released by the minute contact to begin the next revolution.

There are also very large secondary clocks made for towers and churches, which have special requirements, like the weight of the hands, birds who use them as a perch, wind, etc. (Fig. 21 and 22).

Fig. 21: Tower secondary clock by Campiche of Geneva, end of 19^th century. It is unipolar and based on a typical French dial train with an additional plate on which the electro magnet and the indexing system are fixed. A counter weight serves to balance the minute hand.

Fig. 22: Secondary small tower clock by Moser-Baer. It is polarised with an additional system to block the hands between two impulses in order to protect them against accidental untimely movement. Around 1960.

Favag made a very powerful system with a strong motor driven by the mains, controlled by a secondary clock used as relay. Gent manufactured a system called "waiting-train" for controlling a secondary clock, in which a clock using the Hipp Toggle method of pendulum motor has an unusually heavy pendulum that provides enough power to drive heavy hands. The pendulum is adjusted to beat at a gaining rate and gathers the index wheel until a tooth is masked and the gathering is interrupted. At this point the wheel is "waiting" until released by the armature of an electro-magnet on receipt of accurate impulses from a master clock. The release occurs once in each revolution of the index wheel, i.e. every 30 seconds.

Before going to the next chapter, a mention should be given to ship's clocks (both master and secondary), which are built in a way that the hour hands can be moved forwards or backwards to accommodate the change of time zone.

More secondary clocks (or "slaves") on a separate page.

Synchronous clocks

Here too, one can discuss: are they really clocks? In the same way that most secondary clocks are impulse-meters, synchronous clocks are in fact frequency-meters. They are made of a small synchronous motor, turning at a speed dictated by the frequency of the AC mains, and combined with a wheel train to enable the indication seconds, minutes and hours on a dial (Fig. 23).

Fig. 23: Synchronous clock by Michl, signed Laplace, Czechoslovakia 1920s. It must be started by hand. Thiesen in his famous series of books regards it as the first really usable synchronous clock ever made.

Animation of a Michl clock (draw and push the hand to animate it)

The conditio sine qua non is that the mains must have an absolutely stable and precise frequency, which is now the case. This is not to please the owners of these clocks, but because it is indispensable for the interconnection of electric networks. Don't forget that the frequency is 50Hz in Europe and 60Hz in America. An American synchronous clock will not, therefore, keep time in Europe, whatever the voltage, and a transformer is not enough to solve the problem. One needs to change either the motor or the wheel train.

Apart from these aspects and numerous constructional differences, one can distinguish synchronous clocks in two groups:

· The self-starting ones, which stop when current is interrupted and restart when the current is restored, i.e. running but showing the wrong time. Their supporters claim that interruptions are generally short and that an approximate time is better than no time at all whilst their opponents claim that it is an illusion to know time if it is wrong and that it is better to know that one does not know...

· The clocks with manual starter. These also stop when the current is interrupted but don't start again. It is necessary, therefore, to restart these clocks by hand using a button or lever that one would obviously never do without putting the hands to time at the same occasion.

Arguments like this went like this for a long time, but nowadays quartz clocks and radio-control have brought everybody to an agreement!

Towards the middle of the 20^th century, synchronous-clock manufacturers built many "mysterious clocks", that is, clocks whose hands-motion mechanism is invisible or at least not immediately visible. These clocks are described in the companion article Electric "Mysterious Clocks".

Special and anecdotal systems of construction

Despite the numerous difference of operating principle and constructional design, electrical horologists were not satisfied and felt it necessary to invent some very original additional designs, sometimes interesting, sometimes rather laughable.

Let's begin with a genius, Martin Fisher of Zurich, who in 1899 created the Magneta system (later called Inducta, after his company had been taken over by Landis & Gyr of Zug) (Fig. 24).

Fig. 24: Magneta clock by Martin Fischer of Zurich, around 1905. The inductor (a type of dynamo) is on the left of the picture. Winding is manual. The weight of about 17kg hangs on a steel rope and transmits power by winding a strong buffer spring for the inductor (which needs a sudden and rapid movement to create an electric impulse) as well as a small spring in a barrel for the going train with Graham anchor. Winding should take place daily and a warning system placed in the case closes a contact when the weight needs rewinding, lighting a small indicator lamp. If the clock is not wound the pendulum is deliberately stopped otherwise the secondary clock fails long before the master. This condition arises because when the weight is grounded the elasticity of the steel rope will keep the movement going for a while, but the energy is insufficient to wind the inductor. Later, during Landis & Gyr time, these clocks were all made with electric winding.

His slogan was (translated into English): "Electric clocks without battery and without contact". This is very representative of the problems at that time. Batteries could be unreliable and needed a lot of care; and good ones could not just be bought at the corner's supermarket! Switch contacts became burnt and oxidised, as anti-spark systems (which became usual some time later in the form of a resistor associated to a condenser) had not yet been invented. Fifty years earlier, Wheatstone was the first to describe these problems and his electric clocks were the first attempt at their solution by the use of magneto-electric induction. Wheatstone's clock was a failure because he used the pendulum as the inductor as well as the oscillator.

Fisher's idea was to construct a mechanical clock combined with a separate and properly designed magneto-electric generator between its plates that was driven by a separate train of wheels, and released by the going train of the otherwise conventional clock. Every minute his inductor gave a very short (2-3/100 of a second) pulse of current (reversing polarity each time) to a network of secondary clocks. As a matter of fact, only the network is electrical, not the master clock. The first clocks had to be wound by hand, later they were also equipped with a winding motor. The construction is rather heavy, as the inductor needs a very strong instantaneous power to create sufficient current. The secondary clocks are also very specialised as they must react in a very short time. This is achieved through a buffer spring between the electro-magnet and the wheel-train. Important advice to collectors: all clocks under the Magneta name (apart from the British ones, which are of the Hipp type) are built like this, but not all Inducta clocks, despite the misleading brand name. Later, Landis & Gyr built two ranges of clocks in parallel under the same name and in similar cases: inductor clocks and ordinary motor-rewound clocks with contacts.

At the other extremity of genius, one should mention the well-known Jamin-Zenith patent (1922), a sweet for collectors, but maybe not the most practical chronometric instrument (Fig. 25).

Fig. 25: Jamin-Zenith clock without power reserve, mid 20s. The dilatation wire is in the tube seen on the left. It acts on the pendulum through an elastic lever and a traction wire at the bottom. Contacts are on the top of the pendulum. This constitutes a sort of thermic motor working under 4V AC, independent from the dial, which is again just an oscillation meter.

Jamin-Zenith clock animation.

It is a clock in which the pendulum is maintained in movement by a mechanical impulse - we could have classified it in the corresponding chapter but it is so strange that we prefer to classify it separately - but it is particular in that the impulse is given neither by gravity, an electro-magnet or a spring, but by the expansion and contraction of a heated wire. Each time the wire cools down (1/oscillation) the increase in tension is transmitted to the pendulum in the form of a flick. There are variants with and without power reserve. Needless to say that these clocks are full of caprices and that the right quality of wire is almost impossible to find today.

To this thermic section, we can also add the Pneuora of Junghans. It is a mechanical clock with rewinding by compressed air through a piston. The air is expanded by heating in a special sort of filament lamp where it is heated by electricity thanks to a contact placed in the movement. Thus the transmission between the "motor" and the clock is done by air expansion through a pipe. Secondary clocks were controlled in the same way.

Another clock with a thermic motor is the PUJA made by Karl Jauch, Schwenningen, Black Forest. It is constituted by two pairs of tubes containing alcool. One of these tubes is heated from the bottom so that the alcool flows into the upper tube outside the gravity center and the system starts turning, winding up the spring of a traditional mechanical movement (Fig. 26)

Fig. 26: Puja, about 1940.

Signal systems

We now leave the primary function - to indicate the time in a visual way - and examine the acoustic signalling of time, primarily in factories and schools. This is usually achieved thanks to an additional contact module added to a clock of any type. Mostly, it is one or several disks turning during 24 hours, with holes for small pins at 1 or 5 minute intervals. These pins then close the contact when necessary. The system can be completed with a weekly program or the adjustment of the length of the signal (Fig. 27 and 28).

Fig. 27: Favag Master clock with 2/3s pendulum. Late 1920s. Fitted with additional module consisting of a 24 hour contact wheel for actuating signals which are adjustable in 5 minutes intervals.

Fig. 28: Signal control box by Favag constructed on the basis of a secondary clock mechanism. There are many models, with one or more lines of signals.

Added to synchronous clocks, these systems were also used to switch on the lights or a radio, or in hotels to remind Reception to wake up the customers at the right time (Fig. 29).

Fig. 29: American synchronous clock made for hotels. A warning signal can be adjusted by 5 minute intervals, reminding reception to wake up clients at given times.

Chimes

Chimes are rare in electric horology and mostly associated with rewound clocks. They are then similar to mechanical chimes. They also exist in clocks with electro-magnetic impulses (Bulle-Clock, ATO Fig 30). The hammers are moved by an electro-magnet but the counting is by conventional means as in mechanical clocks.

Fig. 30: Ato electric chime.

Sources of documentation

To contact me personally: viredazepal@bluewin.ch