Friedrich Gessner flourished in Breslau, Germany from 1900 until after 1934. He succeeded E.G. Heidrich ( - 1904) who flourished in Brealau from 1867 to ca. 1900 and was reportedly the chief supplier to the German Army. The two patches on the bell of this horn testify to a history of regular long use. The triangular pattern of the valves was common in the second half of the nineteenth and early twentieth centuries. (See another example by Josef Müller). The double horn of M.Jiracek & Sons is a modern example.

The script in the label is unusual. The characters in the middle of the name would appear to be "ll" but with curious descenders. (Compare these with the "s" and "l" in "Breslau"). Instead they are an engraved version of the German script "long" s,  as shown in the 1855 printed example of "Wissenschaft" (below left) or the Sütterlin schrift (below right). 

            

In comparison a flugelhorn by Gessner is known, and is clearly labeled in cursive script (at right, below).