This summer there came into my hands a copy of the spring issue of the Mittheilungen der Math. Gesellschaft in Hamburg containing a paper on the “Transformationen der hydrodynamischen Gleichungen mit Berucksichtigung der Reibung.”

On examination, I found embodied in the somewhat lengthy communication practically the following method, which I had entered in my notes three years ago when working at the subject. Thinking that it was bound to have been used earlier, I simply preserved it, as likely to prove useful if I were ever called upon to teach Hydrodynamics.