Mounted on a 9" marble base is a small brass cannon, and above that a magnifying glass.  The positioning and focal length of the lens would be designed to light the cannon's fuse.  The placement of the sundial suggests that the device was used to mark the arrival of the noon hour (on sunny days).

This intricate device was custom-made for someone living at a latitude of 59 degrees, 55 minutes, 20 seconds.  My guess would be that the recipient lived somewhere in St. Petersburg, but other locations are possible.

Link.

Addendum:  Some additional searching has revealed that devices such as these were known as "sundial cannons" or "noon cannons."  The best description/photos I've found is at this pdf by the British Sundial Society.