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 | |
|---|---|---|---|
| Keeler, Dr. James Edward | USA | 1895 | 1900 |
| King, Dr. William Frederick | Canada | 1892 | 1916 |
| Kirkwood, Dr. Daniel | USA | 1890 | 1895 |
| Langley, Dr. Samuel Pierpont | USA | 1894 | 1906 |
| Lindblad, Dr. Bertil | Sweden | 1956 | 1965 |
| Loewy, M. Maurice | France | 1901 | 1907 |
| Lowell, Prof. Percival Lawrence | USA | 1916 | 1916 |
| Maunder, Mr. Edward Walter | United Kingdom | 1894 | 1928 |
| McLeod, Dr. Clement Henry | Canada | 1894 | 1917 |
| Mitchell, Prof. Samuel | Canada/USA | 1958 | 1960 |