Judiciary Act of 1789 set the number at six: a chief justice and five associate justices. In 1807, Congress increased the number of justices to seven; in 1837, the number was bumped up to nine; and in 1863, it rose to 10. In 1866, Congress passed the Judicial Circuits Act, which shrank the number of justices back down to seven and prevented President Andrew Johnson from appointing anyone new to the court. Three years later, in 1869, Congress raised the number of justices to nine, where it has stood ever since. In 1937, in an effort to create a court more friendly to his New Deal programs, President Franklin Roosevelt attempted to convince Congress to pass legislation that would allow a new justice to be added to the courtfor a total of up to 15 membersfor every justice over 70 who opted not to retire. Congress didnt go for FDRs plan.
So Andrew Johnson and FDR. But the number of judges changed around many times even beyond them. ---
I don't know my gimmick "Does that sound reasonable to you?"