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 | |
|---|---|---|---|
| Newnham, Right Rev. Jervois Arthur | United Kingdom/Canada | 1895 | 1905 |
| Newcomb, Rear Admiral Dr. Simon | USA | 1891 | 1909 |
| Morrison, Dr. Joseph | Canada/USA | 1891 | 1898 |
| Moore, Sir Patrick | United Kingdom | 1993 | 2013 |
| Monck, Prof. William Henry Stanley | Ireland | 1898 | 1915 |
| Mitchell, Prof. Samuel | Canada/USA | 1958 | 1960 |
| McLeod, Dr. Clement Henry | Canada | 1894 | 1917 |
| Maunder, Mr. Edward Walter | United Kingdom | 1894 | 1928 |
| Lowell, Prof. Percival Lawrence | USA | 1916 | 1916 |
| Loewy, M. Maurice | France | 1901 | 1907 |