The use of "Mr. President" in speeches in the Senate

When Senators are making speeches (as they are as this post goes to press), they often address the presiding officer as Mr. President. Why is this?

Is this a referral to the presider who might be functioning as the President Pro Tempore? Or what?

Yes.

Yes.

Source: http://senate.gov/reference/glossary_term/president_pro_tempore.htm

Actually, not the President Pro Tempore but the president pro tempore, if you catch the distinction.

Parallel it to a Robert’s Rules meeting or committee: the Chairman is the elected official whose job it is to lead the meetings, ordinarily by sitting as the presiding officer of the meeting. But if the elected Chairman wishes to speak in his capacity as a member, or is absent or otherwise unable to preside, another member is tapped to occupy the Chair and preside, and is the interim chairman.

The Vice President is constitutionally President of the Senate. In his absence, the role devolves on the person who by Senate rules and long precedent is chosen for the office of President Pro Tempore of the Senate. In the absence or unwillingness or inability to preside of both men, someone else is selected as the interim president pro tempore, in the same manner as an interim chairman replaces the elected Chairman as presiding officer of the public organization referenced above.

And following longstanding procedure dating back to the early days of the English Parliament and preserved in Congressional rule and custom, all utterances on the floor of the Senate or House, whether a motion, a point of order or privilege, a speech, or whatever, are formally addressed to the person occupying the chair, not to their intended audience – the basic reason being to restrain interpersonal disputes and keep the focus on the good of the country.

Even on the rare occasions when the Vice President actually presides, he is properly addressed as “Mr. President”, since he is being addressed in his capacity as President of the Senate.

Likewise, the presiding officer of the House of Representatives is the Speaker. Nancy Pelosi is the speaker, but most of the time she designates another representative to fill the seat as acting speaker. All speeches are directed to Mr. or Madam Speaker, recognizing that whoever is presiding is acting as Speaker, regardless of whether Rep. Pelosi is filling the chair herself.

A great deal of the time, there aren’t much more than two representatives on the floor of the House, the one making a speech and the acting Speaker listening and trying not to look too bored.

I recall watching C-Span (or maybe CNN) once when something procedural was happening when there would have to be a ruling from the Speaker under House rules. I think it was when Tom Foley was speaker. The representative addressing the House was droning on, Mr. Speaker this, Mr. Speaker that, when he stopped as though there was a small commotion. The camera shifted to show Foley stepping onto the rostrum and replacing the guy who was filling the seat. The representative resumed his speech with a distinctly more emphatic "Mr. Speaker. When he was done, Foley made his ruling from the rostrum, and shortly thereafter descended, leaving the chair to another.

Thank you all for your contributions. Wonderful job.