It was not, however, until the beginning of the eighteenth century that the crop of electrical discoveries began to increase considerably: among these was the recognition of the dual nature of electricity, by the Frenchman, Dufais, and the chance invention of the Leyden jar (made simultaneously by the German, von Kleist, and two Dutchmen, Musschenbroek and Cunaeus). The Leyden jar brought electrical effects of quite unexpected intensity within reach. Stimulated by what could be done with electricity in this form, more and more people now busied themselves in experimenting with so fascinating a force of nature, until in the second third of the century a whole army of observers was at work, whether by way of profession or of hobby, finding out ever new manifestations of its powers.