@article{MAN_1874__7_156659,
     author = {Sturm},
     title = {Ueber {Normalen} an algebraische {Fl\"achen}},
     journal = {Mathematische Annalen},
     pages = {567--582},
     year = {1874},
     volume = {7},
     language = {de},
     url = {http://geodesic.mathdoc.fr/item/MAN_1874__7_156659/}
}