For more than two centuries after its inception the Newtonian view of the world ruled supreme, to the point that scientists developed an almost blind faith in this theory. And for good reason: there were very few problems which could not be accounted for using this approach. Nonetheless, by the end of the 19th century new experimental evidence difficult to explain using the Newtonian theory began to accumulate, and the novel theories required to explain this data would soon replace Newtonian physics. In 1884 Lord Kelvin in his Baltimore lectures already mentions the presence of ``Nineteenth Century Clouds'' over the physics of the time, referring to certain problems that had resisted explanation using the Newtonian approach. Among the problems of the time (not all were mentioned by Kelvin) were
The first quarter of the 20-th century witnessed the creation of the revolutionary theories which explained these phenomena. They also completely changed the way we understand Nature. The first two problems require the introduction of the Special Theory of Relativity. The third item requires the introduction of the General Theory of Relativity. The last two items can be understood only through the introduction of a completely new mechanics: quantum mechanics.
As a result of these developments the formalism developed by Newton lost its fundamental character. It is of course still a perfectly good theory but with a very well defined range of applicability. As mentioned previously, this does not imply that Newton was ``wrong'', it merely implies that his theories, although accurately describing Nature in an impressive range of phenomena, do not describe all of it. The new theories that superseded Newton's have the virtue of explaining everything Newtonian mechanics did (with even greater accuracy) while extending our understanding to an even wider range of phenomena. In this chapter I will describe the growth of the theory of electricity and magnetism which was to be fundamental to the development of Special Relativity.
The replacement of Newtonian mechanics was driven by the data that required the replacement of Newtonian physics by these more fundamental ones; the theories of relativity and quantum mechanics together explain all the phenomena probed to date, but they might be replaced in the future by others providing a yet deeper understanding of nature. These new theories will have to explain everything relativity and quantum mechanics do and provide experimentally verifiable predictions which are subsequently confirmed.