Lemaitre's cosmology

The paper presents Lemaitre's contribution to the modern views on the Universe. His participation in one of the greatest scientific revolutions - in the transition from static to the expanding picture of the Universe - is briefly outlined. Lemaitre's hypothesis of the Primaeval Atom has initiated the nucleosynthesis problem in cosmology. The existence of the relic radiation has been predicted on the basis of this hypothesis. Lemaitre, however, mistakenly identified the predicted radiation with the cosmic rays. Further history of Lemaitre's cosmological model is briefly reported. (author)