Swiss rare silver lever poor man’s tourbillon watch Circa 1900

Silver open faced lever pocket watch by Courvoisier Frères
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A Swiss silver open faced poor man’s tourbillon pocket watch according to Swiss Patent No. 30754 of Paul Loichot, circa 1900. Frosted gilt full plate movement, a club tooth lever escapement, screw compensation balance, engraved U.S. Pat. appl. for D.R.P. ang. Pat. N. 7888/1905, Brevettato R.A.208.N.232, Btè S.G.D.G. 30754.
The engine turned case with an engraved vacant cartouche on the back. Silvered engine turned dial, small eccentric time indication in the upper half with radial Arabic hour numerals, outer minute dots and blued spade hands, an aperture for the visible tourbillon with an engraved balance bridge.
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Diameter: 54 mm
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Weight: 94 g
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Signed: Courvoisier Frères Mobilis La Chaux-de-Fonds
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Courvoisier Frères 
Henri-Louis and Philippe Auguste Courvoisier traded from 1842 on under the name Courvoisier Frères. When more brothers joined the partnership in 1882, they changed the company name to “Courvoisier Fils”. Specializing in high quality watches, they were commissioned by the city of La Chaux-de-Fonds to create a watch for the Prussian King William IV; at the time, this ultra flat watch was supposedly the thinnest in the world. The tourbillon movement invented by the Swiss Paul Loichot (which he turned in the case so it would be visibly face sided) was patented for the Courvoisier brothers on July 4th, 1905, under the number 19062 and the name “Mobilis”.
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Tourbillon
A system devised and patented by Abraham-Louis Breguet in 1801 to compensate for errors of rate caused by the Earth’s gravitational force in upright positions. The escapement is mounted in a revolving cage with the regulating organ (balance) at the center.

The escape wheel pinion turns about the fixed fourth wheel. The cage generally revolves once a minute and, in doing so, compensates for errors of rate caused by the vertical position in which pocket watches spend most of their time.

This delicate and complex structure is one of watchmaking’s most ingenious mechanisms. A simplified and more robust alternative is the carrousel, where the cage is driven not by the fourth wheel but by the third wheel. A tourbillon can contain a lever or a detent escapement.