D’Alembert counted as physics in general disciplines such optics, acoustics, positional astronomy, cosmology, magnetism and electricity. For the sake of space, this chapter deals with optics and electricity only. A good deal of the optical works, concerned the theories of propagation of light, with those of undulatory character that required complex mathematical treatments and the use of partial differential equations, becoming a fertile ground for mathematical physics. The experience with which the theories were compared was mostly based on experiments conducted in the 17th century by Newton and Huygens. Relevant new experimental work, on a quantitative basis, was carried out only relatively to what is today known as photometry with Bouguer and Lambert. The creation of the 18th century was the science of electricity. It assumes in the chapter the paradigmatic role of the development of the experimental sciences starting from the ascertainment of the phenomena at a qualitative level—remaining partially in the footsteps of the traditional natural philosophy—up to their quantification. The number and quality of experiments on electricity grew dramatically, especially after the 1750s when the discovery of the Leyden jar made it possible to accumulate large charges. After a brief mention to the situation in the 17th century, the chapter passes to the examination of the English experimenters and the continental ones to stop before Alessandro Volta’s studies at the end of the century.