Particular importance is attached to volume I of this work in which Euler rejects the corpuscular theory of light, constructing his own theory by which the cause of light is attributed to peculiar oscillations of ether. The same volume contains his tables of the sun and moon, as well as a discussion of the problems of perturbations. The first Euler theory had an important practical consequence for T. Mayer, an astronomer from Göttingen, compiled, according to its formulas, lunar tables that enabled the calculation of the position of the moon and thus the longitude of a ship with an exactness previously unknown in navigation. The British Parliament had announced as early as 1714 a large cash prize for the method of determination of longitude at sea with error not to exceed half a degree, and the prize was shared by Mayer and Euler in 1765. Euler's discussion of the relative character of motion and of the relationship between mechanics and optics forms the earliest examination of special and general relativity.