ALS, one page, 7.75 x 8.25, November 12, 1918. Handwritten letter to Dr. Ludwik Silberstein, in full: "I have read your MS with the greatest interest. It is a real pleasure to know that there is a projection treatment of vectors. You do not, in the MS you send me, state the principle of your construction, which is simply to substitute an arbitrary line for the line at infinity. The treatment of scalar coefficients, as we agreed when we met, is identical with the usual method of introducing projection coordinates, but the idea of connecting it with vector analysis is, so far as I know, entirely new. Many thanks for the relativity paper, which I am ashamed to confess I have not yet found time to read amidst the distractions of these days. It is extraordinarily bold of you to take up the 'marmalade problem,' but I hate to think of your time being spent on such a trivial matter." Silberstein notes the dates of receipt and reply on the reverse. In fine condition.
From the collection of physicist Ludwik Siberstein.