The wives of knights should be addressed as "Lady B." or "Lady C.," according to the surnames of their husbands: thus, "Sir John Blank's" wife should be addressed as "Lady Blank" by the upper classes, and as "My Lady" or "Your Ladyship" by all other classes.
In addressing Foreigners of Rank colloquially, the received rule is to address them by their individual titles and surnames.
A prince or princess should be addressed by their full title: thus, "Prince Munich," or "Princess Munich," by the upper classes. Persons intimate with them usually address them as "Prince" or "Princess," as the case may be.
In the case of a prince being a younger son, and not the reigning head of the house, his christian name is generally used after his title when addressing him: thus, "Prince Louis," in lieu of "Prince" only. The same remark applies to the unmarried daughters of princes. They also should be addressed by their christian name, in addition to their title of "Princess," by the aristocracy and gentry, and as "Your Serene" or "Your Imperial Highness," according to their birth and title, by all other classes.
A French duke should be addressed by his surname, with the addition of monsieur: thus, "Monsieur de Rouen," by the upper classes, and as "Monsieur le Duc" by all other classes.
A French duchess should be addressed by her surname, with the addition of madame: thus, "Madame de Rouen" by the upper classes, and as "Madame la Duchesse" by all other classes.
A marquis should be addressed by his surname, with the addition of monsieur: thus, "Monsieur de Harfleur" by the upper classes, and as "Monsieur le Marquis" by all other classes.
A marquise should be addressed by her surname, with the addition of madame: thus, "Madame la Harfleur" by the upper classes, and as "Madame la Marquise" by all other classes.
A comte should be addressed by his surname, with the addition of monsieur: thus, "Monsieur de Montpellier" by the upper classes, and as "Monsieur le Comte" by all other classes.