This is a superb Boosey Eb Tenor horn (in the US it is called an Alto horn).  The serial number of 35912 on the 2nd Valve and 40330 on the bell is indicative of a date of manufacture of approximately 1890-1891.    Despite its age, it still has a remarkably clear and centered sound.  The silver plating is nearly 100% and ready to  get back into the band. The bell is  is inscribed:

(Boosey trumpet logo)