@misc{indiciae70c16c03c490,
  title = {Preliminary Note on Nebular Proper Motions.},
  author = {H D Curtis},
  year = {1915},
  doi = {10.1073/pnas.1.1.10},
  url = {https://pubmed.ncbi.nlm.nih.gov/16586573/},
  note = {Source identifier: 16586573}
}