ABSTRACT
The photoelectric effect was discovered accidentally Karlsruhe in 188/ Heinrich Lenard's mentor, during the initial phase of his celebrated work on Maxwell's electromagnetic waves. We have touched on the circumstances surrounding the discovery earlier, but perhaps a somewhat fuller recapitulation does not hurt at this point. The experimental arrangement is depicted by Hertz himself in figure 12.1. Sparks vvere generated in the gaps d and f Riihmkorff coils a and e, powered the common Bunsen cells b. To observe faint in the gap f, at first shielded against strong ambient light by enclosing the gap in a black box. In so he soon found that the gap must be shortened to allow sparks to pass. At first annoyed by the effect, Hertz 'had no intention of allowing this phenomenon to distract my attention from main object I in view, but occurred in such a definite and way that could not altogether neglect it' Because sparks were known to ultraviolet concluded that ultraviolet light from the primary spark gap facilitated the passage of sparks in the secondary gap. (The black box absorbed the radiation, hindering production of the secondary spark.) Hertz also found that the cathode surface of the spark gap was the sensitive spot.
