I will confine myself to the 19th and 20th Centuries. In pre-French Revolutionary Europe, there were so many rules relating to social hierarchy, that it should be a separate discussion. I will also preface this by observing that Americans, especially in the first half of the 19th Century, were notorious for their rough manners, and the presence of hats on men in theaters, homes and the floor of the US Senate, was commented upon unfavorably by foreigners.

Generally, for the 19th Century man, the hat remained on outdoors, and in fact, a man outdoors without a hat would be a subject of comment (sorry dashing young Hollywood hunks). However, once indoors, the topic gets a little muddier.

The decider seemed to be the public/private nature of the space. In a public space like a train station, hotel lobby, a saloon or a public dance hall, the hat seemed to usually remain on. It is very striking in the numerous paintings of the Moulin Rouge in Paris, that all the men seem to have their top hats glued to their heads, even when sitting at tables with respectable ladies. The only thing that seems to get them off is a swift kick from a high stepping can-can dancer.

The same hattedness seemed to apply to patrons at retail establishments. The customers kept their hats on, though the staff generally did not wear hats while working.

However, in more respectable spaces like restaurants (as opposed to chop houses), where ladies were present, and men were seated, the hats seem to have been generally removed.

Orators should also remove their hats while speaking--even when outdoors. This proved fatal for President W.H. Harrison. In theaters also, hats should be removed, if only out of consideration for those sitting behind.

Now, in private spaces, the rules were different. In a home, a hat was generally removed. The same would seem to also apply to private clubs.

Now, relevant to common current "dress-up" activities, hats should not be worn in a private or subscription ball (like the Social Daunce Irregulars Victorian Ball), though hats could be worn if dancing outdoors.

Note that the same rules apply to military and non-military gentlemen.

The other time when hat-etiquette becomes an issue is when a gentleman encounters a lady. I will address this in a future post.