GAUSS An SPEHR, 9. Juni 1830 .
Varia. Atlas des Erdmagnetismus Bd. 12, GDML_Books, (1929), p. 101 / Harvested from
Access to full text 
@article{PPN236060120+dmdlog70,
     title = {GAUSS An SPEHR, 9. Juni 1830  .},
     booktitle = {Varia. Atlas des Erdmagnetismus Bd. 12},
     series = {GDML\_Books},
     year = {1929},
     pages = {101},
     url = {http://dml.mathdoc.fr/item/PPN236060120+dmdlog70}
}

 (éd.). GAUSS An SPEHR, 9. Juni 1830  ., dans Varia. Atlas des Erdmagnetismus Bd. 12, GDML_Books,  (1929), p. 101. http://gdmltest.u-ga.fr/item/PPN236060120+dmdlog70/