41 For all that he did to render more precise the Christian definition of social rights and duties, no small recognition is due to Our late Predecessor, Pius XII. On Pentecost Sunday, June 1st, 1941, he broadcast his message "to call to the attention of the Catholic world a memory worthy of being written in letters of gold on the Church's Calendar: the fiftieth anniversary of the publication of the epoch-making social encyclical of Leo XIII, Rerum Novarum ," (l6) and "to render to Almighty God from the bottom of Our heart, Our humble thanks for the gift, which... He bestowed on the Church in that encyclical of His vicar on earth, and to praise Him for the lifegiving breath of the Spirit which through it, in ever-growing measure from that time on, has blown on all mankind.'' (l7)
Source: Mater et Magistra (Vatican.va)