@misc{indiciae989145a2386e,
  title = {The computation of second vertical derivatives of geomagnetic fields},
  author = {Roland G. Henderson and Isadore Zietz},
  year = {1949},
  doi = {10.1190/1.1437558},
  url = {https://pubs.usgs.gov/publication/70215625},
  note = {Source identifier: 70215625}
}