These different historical points established, let’s see what were the systems of this time.
They are very similar to each other: a mass, returning in place by a spiral-shaped spring, is pivoted on one side of the plate. A ratchet is integral with the axis of this mass; it is placed inside a small drum with ratchet teeth cut in the opposite direction. A pawl system therefore allows this toothed drum to rotate only in one direction, that is to say when the mass descends. This drum generally carries a pinion in connection with a reduction gear and a large wheel placed on the barrel shaft, which easily raises the spring.
As a general rule, the watch could not be wound otherwise than by shaking it, there was no winding square for the key. What were the means used at that time to prevent the overvoltage of the mainspring?
All the builders of the eighteenth century were content to find a system that stops the mass when the spring is fully wound. The systems certainly differ, but the principle is generally the same: the barrel shaft is threaded between one of its pivots and the journal of the barrel itself. On this thread is screwed, quite freely, a disc filed in segment. The barrel carries a stud, generally a screw, which is placed inside the segment. When the watch is running, the barrel turns and the stud forces the disc to descend. On the other hand, when the watch is wound, the stud remaining fixed, unscrews the disc which goes up. Going up, this disc lifts a large spring carrying at its end a stop which comes to stop the mass in different ways. Sometimes it’s just simple braking,
THE MOST OLD KNOWN MOVEMENT
Let’s take a look at some perpetual watches from the 16th century.
The oldest movement, reassembled by the tremors that the Geneva Clock Museum has (section of the Museum of Art and History), is a piece signed Breguet in Paris. We can not say that this movement was well from the hand of the great master watchmaker, his name having been inscribed many times on the ordinary watches of dishonest competitors. However, this movement has some interesting features
While most shaking watches have a cylinder escapement, most often with a brass cylinder wheel, this movement still has the encounter wheel escapement. However, the first watches that Breguet built were by the yard, and since his perpetual watch dates from the start of his career, it is quite possible that this piece was indeed one of the first that he built.
On the other hand, Sir David Salomons, in his work on Breguet, says about the perpetual watch: “This watch has two motor springs which are wound up by the up and down movement of a weight in platinum or in gold and platinum , which moves when walking; about a quarter of an hour is enough for the complete reassembly ”.
Now, this movement that we describe has two barrels, while all the pieces that we will see later have only one. What could these two barrels be used for? One would think that the two motor springs were intended to increase the driving force, or the duration of the running of the watch. It is not so. On a certificate for a Breguet watch, it is stated that the existence of two barrels has neither of these destinations. What we have been looking for, says Solomons, is the reduction of friction on the pivots of the center pinion. In the case of a barrel, the pinion is pushed back with considerable force. If a barrel is placed on opposite sides, so that it rotates the pinion in the same direction, this pressure on the pivots is removed. In some marine chronometers, Breguet used four barrels to reduce friction and equalize force. It therefore follows that the friction is reduced, which contributes all the more to the perfection and to the good result. One would hardly be tempted to follow this theory these days.
Note that the aforementioned movement, pillars and escapement wheel meeting, has no rocket, as is usually the case with this escapement. One of these barrels meshes with a cog of five pinions and four small diameter wheels. The “nose” of a spring is introduced into the wings of the last pinion and has the effect of a jumper.