The rules governing the election and appointment of Senators were established under Article 1, Section 3 of the Constitution and modified by the 17th Amendment, ratified on 8 April 1913:
Article 1, Section 3.
Clause 1:
The Senate of the United States shall be composed of two Senators from each State, chosen by the Legislature thereof, for six Years; and each Senator shall have one Vote.
Clause 2:
Immediately after they shall be assembled in Consequence of the first Election, they shall be divided as equally as may be into three Classes. The Seats of the Senators of the first Class shall be vacated at the Expiration of the second Year, of the second Class at the Expiration of the fourth Year, and of the third Class at the Expiration of the sixth Year, so that one third may be chosen every second Year; and if Vacancies happen by Resignation, or otherwise, during the Recess of the Legislature of any State, the Executive thereof may make temporary Appointments until the next Meeting of the Legislature, which shall then fill such Vacancies.
Amendment XVII:
The Senate of the United States shall be composed of two Senators from each State, elected by the people thereof, for six years; and each Senator shall have one vote. The electors in each State shall have the qualifications requisite for electors of the most numerous branch of the State legislatures.
When vacancies happen in the representation of any State in the Senate, the executive authority of such State shall issue writs of election to fill such vacancies: Provided, That the legislature of any State may empower the executive thereof to make temporary appointments until the people fill the vacancies by election as the legislature may direct.
This amendment shall not be so construed as to affect the election or term of any Senator chosen before it becomes valid as part of the Constitution.
Name | William Maclay | | Robert Morris | Seat Vacant | Albert Gallatin | Seat Vacant | James Ross | William Bingham | John Peter G. Muhlenberg | George Logan | Samuel Maclay | Andrew Gregg | Michael Leib | Abner Lacock | Jonathan Roberts | Walter Lowrie | Seat Vacant | William Findlay | William Marks | Isaac D. Barnard | William Wilkins | George M. Dallas | Seat Vacant | Samuel McKean | James Buchanan | Seat Vacant | Daniel Sturgeon | Simon Cameron | James Cooper | Richard Brodhead | Seat Vacant | William Bigler | Simon Cameron | Edgar Cowan | David Wilmot | Charles R. Buckalew | Simon Cameron | John Scott | William A. Wallace | James Donald Cameron | John I. Mitchell | Matthew S. Quay | Boies Penrose | Seat Vacant | Matthew S. Quay* | Philander C. Knox | George T. Oliver | Philander C. Knox | William E. Crow* | George Wharton Pepper | David A. Reed | William S. Vare | Joseph R. Grundy | James J. Davis | Joseph F. Guffey | Francis J. Myers | Edward Martin | James H. Duff | Joseph S. Clark | Hugh D. Scott, Jr. | Richard S. Schweiker | H. John Heinz II | Arlen Specter | Harris Wofford | Rick Santorum | |
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* This column indicates the county in which the Senator's political base was located. In certain cases, this was a judgement call.
* Matthew S. Quay was appointed by the governor to fill the vacancy occasioned by the failure of the legislature to elect a Senator in 1899. The appointment was rejected by the Senate. Quay was elected by the legislature in 1901.
* William E. Crow was appointed on 17 October 1921 by the governor to the vacancy occasioned by the death of Philander Knox, who died on 12 October 1921. Crow, in turn, died on 2 August 1922 and was replaced by David A. Reed. Counting the death of Boies Penrose on 31 December 1921, who was replaced by George Wharton Pepper, Pennsylvania lost three U. S. Senators within the space of ten months.
You can secure brief biographical sketches and pictures of Senators at http://bioguide.congress.gov/biosearch/biosearch.asp
