The last decades of the eighteenth century and the first of the nineteenth were a period of profound change politically, socially, economically, and industrially, and not less scientifically. The scientific renaissance had come in the seventeenth century and culminated in Newton. The succeeding period had sufficed to develop his immortal work and to collect a vast array of facts in the descriptive sciences. At the same time the spirit of positive knowledge had been applied to the steam engine and the arts, and in very different directions had influenced the work of Voltaire, Rousseau, Gibbon, Adam Smith, and many others. However they may have differed among themselves, all these men felt the new forces, and responded to them with novel criticism of religion, society, history, and political economy.

Lavoisier had provided the instruments and methods for a revolution in chemistry quite as great as Newton’s in physics. But chemistry differs very greatly from physics in the applicability of mathematics, and a vast experimental edifice had to be raised before, toward the end of the nineteenth century, anything like the completeness of the Newtonian mechanics could be attained in the younger science. Moreover the atomic theory had to be developed, had to be interwoven with the kinetic theory of gases which sees the molecules in endless motion, had to be extended with the help of geometry, before this was possible. Still, a new tendency had formed, which now has become one of the steadiest streams of scientific progress.

Following upon the work of Franklin and Coulomb and many others, the discoveries of Galvani and Volta, of Oersted and Ampère, and above all, of Faraday,〖H. C., XXX, 7-170.〗 in electricity, providing batteries and currents, showing the relationship of electrical to magnetic, chemical, optical, mechanical, and thermal phenomena, constituted another tendency, and both of these have had a profound influence upon the arts. Young and Fresnel created a new science of light. Heat became yearly more important with the development of the steam engine and the growth of physiological and electrical science. The work of Sadi Carnot, Mayer, Joule, Helmholtz,〖H. C., XXX, 173-248.〗 Lord Kelvin,〖H. C., XXX, 251ff.〗 and others led, in the middle of the century, to the principles of thermodynamics, and to the laws of the conservation and degradation of energy.

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