In the second half of the 19th century scientists thought that whole space was filled with some substance - the ether. They thought that electromagnetic waves needed some medium to propagate in as they imagined them as some kind of mechanical waves. In order to let the waves propagate as quickly as they do (that is with the speed of light) ether had to be very inflexible, but besides it had not to react with celestial bodies moving in it. Creating and using the hypothesis of such a strange substance can be justified by the fact that such a model explained many of the experimental occurrences in the field of electromagnetism. Even Maxwell himself in his researches of electricity and magnetism assumed the existence of the incompressible and elastic ether. In 1905 Albert Einstein finally disposed of the ether hypothesis.