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 | |
|---|---|---|---|
| von Struvé, Dr. Otto Wilhelm | Russia | 1894 | 1899 |
| Williams, Mr. Arthur Stanley | United Kingdom | 1909 | 1938 |
| Winder, Mr. Daniel K. | USA/Canada | 1890 | 1891 |
| Wolfer, Prof. Alfred | Switzerland | 1904 | 1931 |
| Woolley, Dr. Richard v.d.R. | United Kingdom/South Africa | 1961 | 1986 |