Presidential Succession Act of 1792
From dKosopedia
Law passed in 1792 by Congress which provided for a line of Presidential succession in the case of an absence of both the President and the Vice President. According to the Act, the President pro tempore of the Senate would be first in line after the Vice President, followed by the Speaker of the House. In either case, the official would serve only until a special election was held to fill the vacancy.
This ordering was in effect until 1886, when the Speaker of the House and President pro tempore were replaced by the President's Cabinet. They re-entered the line of Presidential succession in 1947 in the reverse (and current) order, with the Vice President being followed by the Speaker of the House, then the President pro tempore, then the Cabinet.