The lightning rod which tops the dome is a story in itself. It is a "Franklin" rod, constructed and grounded to Benjamin Franklin's specifications. In some respects, the useof this type of lightning rod was also a political statement, expressing support for Franklin's theories on protection of public buildings from lightning strikes and the rejection of the opposing theories supported by King George III. The pointed lightning rod atop such an important new public building was a powerful symbol of the independence and ingenuity of the young nation.
As an architect trained in London and with a brother who had a bookshop in Annapolis, Clark would have been familiar with the writings of Benjamin Franklin. In addition, Charles Willson Peale confirmed Clark's design. On July 14, 1788, he and his brother went to Philadelphia to see His Excellency Doctor Franklin to ask his opinion on the efficacy of lightning rods on the State House. They were unable to see Franklin, but did see Robert Patterson and David Rittenhouse, both eminent authorities on the physical sciences. Peale reported that Mr. Rittenhouse was of the opinion that "if the points are good and near anough the Building and the part going into the ground so deep as to get into soft earth no danger is to be apprehended, but if the end could be put in water of a Well it would be best."
The engineering of the lightning rod and the acorn which holds it in place represents an astonishing achievement. Protruding 28' into the air, the rod is anchored at its bottom to the top of the dome. It then runs through the pedestal and the acorn and is surmounted by a copper weather vane. The acorn and pedestal have served to stabilize the Franklin rod and hold it in place for more than two centuries of extremes of Maryland weather.
The dome which Clark designed and built for the State House has been the defining landmark of the Annapolis skyline for more than 225 years. It was also, for many years, a popular spot from which to observe the city and the Chesapeake Bay beyond. Charles Willson Peale planned a dramatic cyclorama of Annapolis with eight views from the dome and a centerpiece drawing of State Circle from Cornhill Street. Only the drawing of the State House was completed and published in 1789. Thomas Jefferson spent a most enjoyable three hours in September 1790 on the balcony of the dome with James Madison, Thomas Lee Shippen and an Annapolis friend who entertained them with the gossip related to each of the houses they could see from their perch above the town.
In 1996, an examination of the dome and the acorn revealed that almost all of the material in the acorn, its pedestal and the lightning rod was original from the 18th century. During the summer and fall of 1996, the acorn was removed and replaced by a new one. The new acorn is constructed of 31 pieces of cypress made by craftspeople from around the state and is clad in copper and gilded on the top, like the original. The original lightning rod has remained intact and continues to serve as it has for more than 225 years, although a steel sleeve has been placed around it inside the new acorn to strengthen it.
