During the beginning of the 19th century, especially in Germany, there was a romantic reaction against the mechanistic and materialistic philosophy behind scientific development. The influence of Hegel, whose philosophy of nature was based not on experimentation but on a priori concepts, remained strong throughout the first half of the century in Germany. Scientists such as the great German poet Johann Wolfgang von Goethe tried to find scientific explanations by using general philosophical principles. For example, Goethe fought Isaac Newton’s idea of white light being a mixture of colors, claiming that in principle white light should be simpler and purer in composition than colored light.

The idea that science would ultimately explain all phenomena in nature became stronger. The Naturphilosophie eventually lost influence and was replaced by materialism: Kraft und Stoff (force and matter) became the tenet of the new philosophical outlook. Matter and force, and later, matter and motion, were viewed as the ultimate explanations of reality. The French philosopher Auguste Comte became the strongest spokesman of the philosophical school termed positivism. He viewed science as the most advanced stage of knowledge. In positivism the use of scientific principles to explain the laws governing all phenomena supersedes the two earlier stages of knowledge: a theological or imaginative stage in which phenomena are explained by divine powers, and a metaphysical or abstract stage in which phenomena are explained by general philosophical ideas.

Near the end of the century, Ernst Mach put forward ideas that were to have their most profound effect through their influence on Albert Einstein. He did not think a metaphysical stage was needed. Mach looked to sensation as the basis of all knowledge and was skeptical of attempts to establish cause and effect with certainty. His critique of Newtonian theory, because it is based in concepts of absolute time and space, was perhaps the most important part of his philosophy for science. Initially he doubted that atoms could be real because they were not directly observable in the 19th century, but some think he eventually accepted that evidence could establish the reality of entities that could not be established on the basis of human sense.

The division between science and philosophy was not as clear in the 19th century as it is today. In Cambridge in 1883,William Whewell suggested to the British Association for the Advancement of Science that their members be called scientists, a term analogous to the word artist for those who practice the arts. Today we would call few of those members scientists, since most were amateurs or supporters of science. The word gradually caught on, however, and began to displace “natural philosopher.” Part of the development of the concept of scientists and of a scientific method resulted from a change during the century in how students learned science. Laboratories were set up at the University of Edinburgh and, later, at other universities.William Thomson (later Lord Kelvin) was the first to have his physics students at the University of Glasgow conduct experiments. Experiments were clearly seen as science, while philosophy was thought to be based on pure reason.