Honorary Membership was limited to 10 from 1890-1900, and to 15 from 1901 onwards. Corresponding Membership was a lesser class of Honoris causa membership in the early years. A few honorary members, such as Barnard, were first made corresponding members for a short time before being recommissioned as honorary members.
| Nation(s) | Start |
End |
|
|---|---|---|---|
| Burnham, Prof. Sherburne Wesley | USA | 1891 | 1921 |
| Brashear, Dr. John A. | USA | 1901 | 1920 |
| Pickering, Dr. Edward Charles, OPM | USA | 1894 | 1919 |
| McLeod, Dr. Clement Henry | Canada | 1894 | 1917 |
| Downing, Dr. Arthur Matthew Weld | United Kingdom | 1896 | 1917 |
| King, Dr. William Frederick | Canada | 1892 | 1916 |
| Lowell, Prof. Percival Lawrence | USA | 1916 | 1916 |
| Backlund, Dr. Oskar | Sweden/Russia | 1916 | 1916 |
| Fleming, Dr. Sir Sandford | Canada | 1890 | 1915 |
| Monck, Prof. William Henry Stanley | Ireland | 1898 | 1915 |