_Hypothesis, of the Sea being the grand Source of Lightning,
retracted. Positive, and sometimes negative, Electricity of the
Clouds discovered.--New Experiments and Conjectures in Support of
this Discovery.--Observations recommended for ascertaining the
Direction of the electric Fluid.--Size of Rods for Conductors to
Buildings.--Appearance of a Thunder-Cloud described._
_Philadelphia, September, 1753._