SUNDIAL

Jefferson constructed his sundial in conjunction with Benjamin H. Latrobe in 1809. Jefferson best described his thought process which eventually led to his creation of the sundial. "I had placed the Capital on a pedestal of the size proper to it's diameter, and had reconciled their confluence into one another by interposing plinths successively diminishing. It looked bald for want of something to crown it. I therefore surmounted it with a globe and it's neck, as is usual on gate posts. I was not yet satisfied; because it presented no idea of utility. It occurred then that this globe might be made to perform the functions of a dial. I ascertained on it two poles, delineated it's equator and tropics, described meridians at every 15 degrees from tropic to tropic, and shorter portions of meridian intermediately for the half hours, quarter hours, and every 5 minutes. I then mounted it on it's neck, with it's axis parallel to that of the earth by a hole bored in the Nadir of our latitude, affixed a meridian of sheet iron, moveable on it's poles, and with it's plane in that of a great circle, of course presenting it's upper edge to the meridian of the heavens corresponding with that on the globe to which it's lower edge pointed." After his completion of the sundial, Jefferson stated, "Perhaps indeed this may be no novelty. It is one however to me."

From http://cti.itc.virginia.edu/~meg3c/classes/tcc313/200Rprojs/jefferson_invent/invent.html