Why is the speaker of the house the third in line to be president?

3 U.S.C. 19 (volume 3 of the United States Code, section 19) makes the Speaker of the House the next in line to be president when no vice president is available. That law was put into place in 1947. In prior incarnations, the president pro tempore of the Senate or the Secretary of State were third in line to be president.


If you wanted a deeper "why" answer, you'd need to go do some research into the legislative history surrounding the 1947 act. You'd need to go to a library with the Statutes at Large and the Congressional Record available, since there aren't free electronic versions that go that far back.