@article{JRAM_1859__56_147769,
     author = {H. Heilermann},
     title = {Ueber die {Focalpunkte} der {Fl\"achen} zweiten {Grades.}},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {345--364},
     publisher = {mathdoc},
     volume = {56},
     year = {1859},
     language = {de},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1859__56_147769/}
}