1. A summary of the principles on which this experiment is based, and of the progress of its development may be found in NATURE of July 9, 1914 p. 404.
2. See Proc. camb. Phil. Soc., November 11, 1912, or Proc. Roy. Soc., April 7, 1913.
3. From a book now in the press, to be published by Messrs. and . G. Bell and Sons .