Au milieu des solicitudes and Diuturnum
http://www.vatican.va/holy_father/leo_xiii/encyclicals/documents/hf_l-xiii_enc_16021892_au-milieu-des-sollicitudes_en.html
http://www.vatican.va/holy_father/leo_xiii/encyclicals/documents/hf_l-xiii_enc_29061881_diuturnum_en.html