Extract IN 1917 Professor E. S. Moore, of the School of Mines, Chicago, U.S.A., kindly sent me a photograph together with this note: “I am sending you a photograph of something which may illustrate your bubbles on the australites. Mr. Dudley of the Metallurgy Department was working with a small crucible containing slags and by accident a drop of water fell on the surface, with the result that a bubble was developed, such as you see in the photograph. The photograph is not a very good one; but it will show you what I mean.