1. For example, Z. Phys., 89, 605, 614, 634 (1934).
2. Phil. Mag., 21, 399 (1936).
3. The papers describing Rehbinder's work were given to me on my recent visit to Russia, but I have mislaid them and hence cannot give the reference. I hope later to write a note in Nature describing this very interesting work.
4. Proc. Roy. Soc., A, 175, 290 (1940).