NOTE 
Volume 20 of the Contributions consists of 14 parts, which were 
issued as follows: 
Part 1, pages 1 to 36, May 31, 1917. 
Part 2, pages 37 to 94, August 3, 1917. 
Part 3, pages 95 to 132, June 18, 1918. 
Part 4, pages 133 to 158, October 14, 1918. 
Part 5, pages 159 to 172, October 1, 1918. 
Part 6, pages 173 to 220, August 29, 1919. 
Part 7, pages 221 to 246, September 9, 1919. 
Part 8, pages 247 to 312, April 29, 1920. 
Part 9, pages 313 to 382, April 29, 1920. 
Part 10, pages 383 to 436, June 20, 1921. 
Part 11, pages 437 to 452, January 26, 1922. 
Part 12, pages 453 to 490, January 9, 1922. 
Part 13, pages 491 to 554, July 19, 1924. 
Part 14, pages 555 to 588, April 27, 1925. 
IV 
