TLS in German,, one page, 8.25 x 5.75, September 2, 1966. Letter to Mr. Birker, in part (translated): "My book Dynamics of Crystal Lattices appeared in 1917 by Teubner in Leipzig and has probably long gone out of print. If you want to learn something modern about crystal lattices, get my newer book (with Kun-Huang) Dynamics of Cristal Lattices, Clarendon Press, Oxford, 1954. But since you probably do not know anything about all these things, I assume that you only want to have an autograph. But I'm 83 years old and sick and can not write to you personally. So you only have the signature here." In fine condition.
