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 |
|
|---|---|---|---|
| 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 |
| Holden, Dr. Edward S. | USA | 1891 | 1914 |
| Gonzalez de León, Sr. Luis | Mexico | 1903 | 1914 |
| Swift, Dr. Lewis A. | USA | 1903 | 1913 |
| Ball, Dr. Sir Robert Stawell | United Kingdom | 1894 | 1913 |
| Darwin, Dr. Sir George Howard | United Kingdom | 1894 | 1912 |
| Terby, M. François J. | Belgium | 1894 | 1911 |