TABLE OF CONTENTS R.T. Waters
Benjamin Franklin was born in 1706, and was fascinated in his youth by electrical phenomena. In 1732 he founded with his collaborators the Library Company of Philadelphia with the support of the Penn family, and achieved a new insight into electrical science with his definition of a 'single electric fire'. This is equivalent to the free-electron concept, and implies the principle of the conservation of charge.
In 1750 he showed that a needle brought near to a charged conductor caused a spark, but when further away discharged the conductor silently (a mechanism today known as a glow corona). Franklin wrote that: 'this power of points may be of some use to mankind'. Foremost in his mind was to achieve protection against lightning, and in the famous Philadelphia Experiment (performed under Franklin's direction by d'Alibard in France in 1752) point discharges were used to prove the electrification of the thundercloud and to identify correctly the direction of the field formed by the cloud charges [1]. The public effect of these successes was great, and they were regarded as the most important work since Newton.
Franklin, in fact, had envisaged from his laboratory tests two complementary concepts for the function of a lightning rod:
the possible harmless discharge of the cloud
the attraction of the flash and the conduction of the charge safely to ground.
Although the first process is not feasible, the second is very efficient, at least for negative lightning. Franklin [2] clearly...
