This unusual clock is a solar cannon. It's a sundial that fires a tiny cannon when the heat of sunlight, concentrated wih a lens, detonates gunpowder. In a 1903 treatise on solar energy, Charles Henry Pope wrote:
In the issue of the American of December 30, 1882, an account is given of the "solar cannon of the Palais Royal in Paris, France, which is fired by the heat of the sun at noon, concentrated by means of burning glass, falling on the powder priming of the cannon."
Link -via Pocket Pistols, Historic Firearms, & Curiosities | Photo: Little Gun