This section is from the book "The Constitutional Law Of The United States", by Westel Woodbury Willoughby. Also available from Amazon: Constitutional Law.
The Supreme Court is at present composed of nine justices - eight associate justices and one chief justice. It sits at Washington, D. C, and holds annual terms beginning in October and lasting till the end of May.4
4 From 1789 to 1807 there were six Supreme Court Justices; from 1807 to 1837 seven; from 1837 to 1863 nine; from 1863 to 1866 ten; from 1866 to 1869 seven; since 1869 nine, the present number. For many years two terms annually were held. A chief justice is only impliedly provided for in the Constitution in that clause which declares that the chief justice of the United States shall preside in cases of impeachment of the President (Art. I. Sec. III, CI. 6). According to Art. I, Sec. VI, CI. 2, no member of either house of Congress may, at the same time be a federal judge, but no constitutional
Each justice of the Supreme Court is assigned to a circuit in which it is required by law that he shall hold court in each district at least once in two years. His services may also be required in the Circuit Court of Appeal of his circuit. In fact, however, since the erection of the Circuit Courts of Appeal the Supreme Court justices sit but seldom in the inferior courts.