What legislative act permanently established the size of the House of Representatives?

The Reapportionment Act of 1929 is the legislative act that permanently established the size of the House of Representatives at 435 members. Prior to this act, the number of representatives could change based on the population counts from the decennial census. The Reapportionment Act created a formula that set the total number of representatives, ensuring consistency in the size of the House and making it easier to manage representation as the U.S. population grew. This act also established a process for reallocating those 435 seats among the states based on changes in population over time, but it firmly capped the total number of representatives, thus stabilizing the structure of the House for future Congresses.

Other options refer to different legislative acts or amendments that do not specifically address the size of the House of Representatives in a permanent way. The Constitutional Amendment of 1789 dealt with various aspects of governmental structure but did not set a specific number for House membership. The Census Act of 1940 focused on procedures for the census rather than the size of the House itself. The Voting Rights Act of 1965 aimed at eliminating racial discrimination in voting, not legislative structure or representation.