When this work first appeared in 1767, electricity was seen as such a minor aspect of natural philosophy that its investigation was not considered a priority for contemporary scientists. The polymath Joseph Priestley (1733-1804) was one of the few who devoted serious effort to advancing the field. Here he charts the history of electrical study from experiments with amber in ancient Greece to the most recent discoveries. The book comprises explanations of the principal theories of electricity - both historical and contemporary - in addition to a selection of well-known experiments carried out by previous researchers. Priestley also details his own experiments, covering such topics as the colour of electric light, the effects of temperature, and even the musical tone of electrical discharges. One of his most successful works, testifying to the clarity of his explanations, the book remains an important text in the history of science.