Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (50 p.m.a.), Mainland China (50 p.m.a., not Hong Kong or Macao), Germany (70 p.m.a.), Mexico (100 p.m.a.), Switzerland (70 p.m.a.), and other countries with individual treaties.
Uploaded a work by E. C. Slipher from [https://articles.adsabs.harvard.edu/pdf/1937ApJ....86..345A The Sodium Content of the Head of the Great Daylight Comet Skjellerup 1927 K.], Astrophysical Journal, vol. 86, p.345 with UploadWizard