1. Mendelssohn and Moore, Phil. Mag., 21, 532 (1936).
2. Keesom and Désirant, Proc. Roy. Soc. Amsterdam, 42, 536 (1939); and private communication.
3. Mendelssohn, Moore and Pontius, VIIe Cong. Int. du Froid, 1, 431 (1936).
4. Daunt and Mendelssohn, Proc. Roy. Soc., A, 160, 127 (1937).