Catholic Church. Pope (1958-1963 : John XXIII). (1959). Encyclical letter (Ad Petri cathedram) of His Holiness John XXIII by Divine Providence Pope to His Venerable Brethren the Patriarchs, Primates, Archbishops, Bishops, and all other local Ordinates that are at peace and in communion with the Apostolic See, and to the clergy and faithful of the Catholic world, concerning the attainment of truth, unity, and peace in the spirit of love. Catholic Truth Society.

Catholic Church. Pope (1958-1963 : John XXIII). Encyclical Letter (Ad Petri Cathedram) of His Holiness John XXIII by Divine Providence Pope to His Venerable Brethren the Patriarchs, Primates, Archbishops, Bishops, and All Other Local Ordinates That Are at Peace and in Communion with the Apostolic See, and to the Clergy and Faithful of the Catholic World, Concerning the Attainment of Truth, Unity, and Peace in the Spirit of Love. London: Catholic Truth Society, 1959.

Catholic Church. Pope (1958-1963 : John XXIII). Encyclical Letter (Ad Petri Cathedram) of His Holiness John XXIII by Divine Providence Pope to His Venerable Brethren the Patriarchs, Primates, Archbishops, Bishops, and All Other Local Ordinates That Are at Peace and in Communion with the Apostolic See, and to the Clergy and Faithful of the Catholic World, Concerning the Attainment of Truth, Unity, and Peace in the Spirit of Love. Catholic Truth Society, 1959.