This level consists of a brass frame supporting a small piece of glass, partially silvered,
that can be held by hand or mounted on a Jacob staff. M. Burel, a French military engineer, developed the form in the early decades of the 19th century. This example dates from the period 1853-1862, when Richard Patten & Son were working in Baltimore, Maryland.
Ref: M. Hachette, "Rapport . . . sur un nivea-réflecteur inventé par M. Burel, lieutenant-colonel au Corps royal du genie," Bulletin de la Societé d'Encouragement pour l'Industrie
Nationale 26 (1827): 275-283.