There is no evidence to suggest that even as late as January 1672, when Newton was elected a Fellow of the Royal Society, anyone (except those unknown few who had in the previous years attended his Lucasian lectures at Cambridge) had any inkling of his new theory of colours. His name exploded on the scientific scene as the inventor and constructor of a new kind of telescope—what later became known as the reflector (which was somewhat misleading compared with its name during the seventeenth century: the catadioptrical telescope). Had the erudition of the London virtuosi been a little broader, they would have known that in fact he was not the inventor of the telescope, even though the precise form he gave it was his. Not only was the idea a hundred years old, during which period it was repeatedly suggested by various writers, but also Newton himself took the idea straight from the most recent of these suggestions, namely that included in James Gregory's Optica promota of 1663. The situation becomes even more ironic when we realize that the new instrument was admired for wrong reasons and on merits that were far from Newton's intentions. Nevertheless, admired it was, and there was a good reason for this: Newton's instrument was in fact the first reflector actually to be constructed and, moreover, for a few weeks (before its mirror became tarnished) it performed quite well. Several astonomers became interested because of the high magnifying power relative to its dimensions (about 7 inches long, with a magnification of 38).

There are several differences between the theories of matter published by René Descartes in 1637 and 1644 which deserve attention. The differences follow from Descartes's well-known identification of substance with spatial extension, and his consequent rejection of the void. Since there was no void space, Descartes argued, a very finely divided subtle matter must extend throughout the universe in order to fill all space not otherwise occupied by the less finely divided ordinary matter. In the 1637 treatises La dioptrique and Les météores Descartes described only one kind of subtle matter, the primary function of which was to transmit the action of light. Yet when he came to write Principia philosophiae (1644), he believed that the subtle matter was divided into two separate elements. One of these remained an aether for light transmission, but the other had lost this property and was believed instead to be active in magnetic effects and in the electrification of glass, and to form part of the substance of flame.

In Italy the physical sciences had several decades of prosperity during the first half of the seventeenth century, largely because of the genius of Galileo Galilei and the efforts of a small constellation of his talented followers. But Galileo died in 1642, and before the end of the 1640s three of the most gifted of his disciples, Castelli, Renieri, and Torricelli, had also gone to a better life, to use the favourite euphemism of the time. Thereafter Tommaso Cornelio at Naples, Giovanni Alfonso Borelli at Messina and later at Pisa, as well as some lesser men, carried on the new science, and in 1657 the scientific enthusiasm of the Grand Duke Ferdinand II of Tuscany and his talented brother Leopold led to the short-lived Accademia del Cimento (1657–67), whose clear-cut and totally empirical programme of experimentation, reported on in 1667 but carried out mainly before 1662, was the last Tuscan flame to rise from the Galilean embers. Physiology and anatomy continued to develop, and north of the Apennines there was activity in astronomy and in optics, but the last was an isolated spark in the general gloom.

In recent years John Herapath has emerged as an important figure in the early history of the dynamical theory of gases. In a series of papers published in 1821 and 1822 he outlined an elaborate theory of the states of matter, specific and latent heats, vapours and gases, culminating in a theory of the gravitational ether. This work was based on the rejection of the caloric theory of heat and was founded instead on the idea that the particles of matter were in constant motion; the forces of caloric were replaced by the transfer of momentum. Herapath's is one of the earliest of dynamical theories of gases to be worked out in any mathematical detail.