E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
The office of chief magistrate in a corporate town.
Below the chair. An alderman who has not yet served the mayoralty.
Passed the chair. One who has served the chief office of the corporation.
The word is also applied to the office of a professor, etc., as The chair of poetry, in Oxford, is now vacant. The word is furthermore applied to the president of a committee or public meeting. Hence
To take the chair. To become the chairman or president of a public meeting. The chairman is placed in a chair at the head of the table, or in some conspicuous place like the Speaker of the House of Commons, and his decision is absolutely final in all points of doubt. Usually the persons present nominate and elect their own chairman; but in some cases there is an ex officio chairman.