The instrument has a cylinder escapement with an unusual, but not entirely unheard of, design.
A standard cylinder escapement (Fig. 36) is made up of a column wheel and a cylinder with a notch. However, this type of escapement was difficult and expensive to manufacture, so from the second half of the 18th century some watchmakers set about making it simpler.
The first part to be simplified was the wheel, which was made completely flat, as shown in the picture below.
The notch was then removed from the cylinder, as can be seen in the model shown in figure 37. This new model was called a 'pig trough cylinder' ('cylindre en auge de cochon' in French).
In view of this, you can't help wonder why this simplified version wasn't adopted by all watch manufacturers who made watches with cylinder escapements.
The simple answer is that this type of escapement was far less efficient than the standard model, as the maximum possible amplitude was far lower.
In the standard model, the notch permitted a larger amplitude, but this meant that the column wheel had to have teeth, making it more difficult to manufacture.
So why did Louis Moinet choose this simplified version of the cylinder escapement? The answer lies in the fact that, due to the unusually high frequency of his compteur (216,000 V/h), this problem simply did not arise.
HOW THE ESCAPEMENT WORKS
The italicised text indicates that these locking phases have yet to be confirmed. It is possible that the cylinder falls directly on the impulse of the wheel, in which case we would move directly from phase 1 to phase 3.
Phase 1: Impulse on exit The impulse plane of tooth 1 of the escape wheel acts on the exit lip of the cylinder, which supports the foliot. Energy is transmitted to the foliot, which continues to oscillate.
Phase 2: Exterior locking Tooth 1 has ended its impulse and left the cylinder. Tooth 2 has fallen on the outer shell of this cylinder. An upward locking angle is created before the cylinder falls back as a result of the action of the wound balance-spring.
Phase 3: Impulse on entry The impulse plane of tooth 2 of the escape wheel has geared with the entry lip of the cylinder, which supports the foliot. Energy is transmitted to the foliot, which continues to oscillate.
Phase 4: Interior locking Tooth 2 has ended its impulse and left the cylinder. It has fallen on the inner shell of this cylinder. An upward locking angle is created before the cylinder falls back as a result of the action of the wound balance-spring. Tooth 3 is now in the position described in phase 1.
REGULATING MECHANISM - FOLIOT/BALANCING-SPRING
We can see from figure 38 that this mechanism is also unusual in that there is no balance, although it does have an easily identifiable standard balance-spring. To achieve such a high frequency (216,000 V/h), the mechanism requires a relatively strong balance-spring for a relatively light regulator (in this case the foliot) – the exact opposite of what Romilly used in his instrument to achieve a low frequency of 3,600 V/h.
The regulator used in Moinet's compteur is a foliot. This term denotes the regulators used in the first mechanical clocks during the 13th and 14th centuries, which at that time were normally associated with the verge or crown-wheel escapement. In this case, the regulator is combined with a cylinder escapement with no notch and a flat wheel. The foliot is a simple bar mounted on a swivel axis.
However, it still contains a system for adjusting the period. Here, on each end we can see that there is a nut mounted on the threaded part of the foliot. By screwing on these nuts, the radius of gyration is reduced, resulting in gain. The opposite is true if they are unscrewed.
A bar has been added to this foliot, forming a cross. This bar helps to lock the foliot when the user measures a period of time, as described in the section on how the compteur works.
CHARIOT FOR ADJUSTING FUNCTIONS
All escapements require highly tuned functions, and the one used in this compteur is no exception. It has exactly the same mechanism as all instruments fitted with this kind of cylinder escapement, namely, a chariot. In the cylinder escapement, the depth of the cylinder in the teeth of the wheel needs to be adjusted on the one hand, and on the other, the drops need to be balanced in order to ensure that they are identical on entry and on exit.
To explain these different points, we will use photographs of a standard cylinder movement with an identical chariot mechanism, presented alongside photographs of the compteur. Figures 40 and 41 show the balance-cock in position in each of the instruments.
The system already includes a base plate (figure 42 shows the one used in the standard movement and 43 the one from the compteur). This plate should be thought of as the chariot, as it holds the balance-cock, foliot and balance-spring, all of which can be moved. On this plate there is a bracket and the lower pivot of the regulator, whether this is a foliot or balance (see arrow). This plate is fitted to the bottom plate, but its heel is positioned slightly above a screw head (see figures 44 and 45), leaving this head partly visible. The screw head is fastened to the plate by a pin (see figures 40 and 41). By adjusting the screw head, the plate and all of the parts attached to it can therefore be moved in all directions.
Finally, figures 46 and 47 show the entire mechanism from 2 different angles, with the balance-cock and balance fitted to the chariot. We can surmise that, by adjusting the screw head, the entire mechanism (and therefore the cylinder) can be moved in relation to the wheel. This would enable the user to both balance the drops and adjust the depth of the cylinder against the wheel in a completely perpendicular and precise manner.
Fig.46 and 47: The entire chariot