French chronometer with spring detent escapement Circa 1880

Probably a graduate’s silver pocket chronometer
–
An exceptional French pocket chronometer, probably a graduate’s piece with spring detent escapement according to Thomas Earnshaw, circa 1880.
Silver tiered case, glazed backside, slightly domed, rose gold pendant, bow, hinges, and shackle. Enamel dial with radial Roman hours, auxiliary seconds, and blued Breguet hands. Full plate movement, keywind, frosted, gilt, chain/fusee, bimetallic chronometer balance with three cylindrical weights and six gold screws, free-sprung blued helical balance spring, chatoned sapphire endstone on balance.
–
Diameter: 60 mm
–
Weight: 166 g
–
Signed: No name