Restoration of a Miniature Patek Philippe
Page 2

A very interesting watch indeed, it has an 18 Kt. yellow gold case and, as you can see, it is signed with the serial number.  This number according to my records would indicate a production date around 1880. 

Not signed by the maker, the movement bears the same serial number on the dial side.  Finish is high quality and the mainspring and barrel in this watch are very unusual.  The movement has a slipping mainspring of the type that is commonly found in modern self-winding watches.   As the watch becomes fully wound the pressure of the inner coils of the mainspring is removed from the outer coil and the tail is allowed to slip from notch to notch.  Also, this is a single piece mainspring that tapers to twice as thick on the outside coil. There is no bridle.

I do not know who invented the slipping mainspring.  Mr. Manuel Yazijian CMW (AWCI Instructor) has observed that Georges Frederic Roskopf used the feature in the late 1860's. I suspect it was invented when a barrel hook failed. It could not have been considered useful until the fusee was discarded.   That would not happen until after the cylinder escapement demonstrated some tolerance to variations in driving force.

The watch winds and sets with the crown and cannot be over-wound because of the slipping mainspring arrangement.  There is no need for a stop-work mechanism with the slipping mainspring.  Watches without recoil click arrangements can be over-wound. Over winding is not a fable. It is also true that cylinder watches can stop running if too much power is applied to the train.  They will stop on the lock because the balance spring cannot overcome the friction of the escape teeth against the cylinder wall when the force is too great.  A tiny watch is especially susceptible to stopping on the lock because the balance spring is so light.