In the 19th century they believed in the absolute motion and the ether, and they were searching for a scientific proof of the motion of the Earth. When Foucaults experiment was done, people still believing that the earth was still wasfinally convinced that it moves instead. But it is well known that in the 20th, thanks to Einstein, this belie in absolute motion has been abandoned: motions are relative, there is no eather and no absolute motion... Yet everybody talks without problems of the motion of the Earth, estabilished by Foucaults pendulum experiment, in terms of the 19th century, even in textbooks. As for me, I have a problem in conciliating modern belief in relativity and relative motions with Foucaults pendulum experiment. Anyone can help? Thank you in advance.