Frankford Arsenal has a sundial which tells time with a spot of light, rather than a shadow.  Unique in the world among such devices, the dial was designed in 1874 by the late Capt. William Price then stationed in the Arsenal.  It was mounted on the muzzle of an old cannon set up vertically on a site near Building 106.  With the war time scrap drive came the dismantling of the dial from its cannon pedestal and the subsequent storing of the dial itself.  Plans are now in the making to remount the dial on a marble pedestal and find a suitable location for it on the Arsenal ground.

In a nutshell, this particular sundial, sometimes called a lens dial, features a lens so mounted as to collect the rays of the sun at high noon and pinpoint them on the plate.

As seen in the Bridesburg Bulletin May 25, 1956