1 6 6 D O C U M E N T S 1 5 0 , 1 5 1 J A N U A R Y 1 9 2 6 150. To Poale Zion[1] Berlin, 3 January 1926 Dear Sirs, You are right to think that I am sympathetic to your charitable organization.[2] However, I have decided to no longer support individual Jewish endeavors in the future, since through such boundless and unwarranted use of my name, any pros- pect for me to continue to exercise influence in matters of central importance is un- dermined. Consequently, I very much regret that I cannot comply with your wishes. Respectfully yours, signed 151. From Rudolf Ladenburg [Dahlem, Berlin,] 5 January 1926 Dear Professor Einstein, Many thanks for your kind communication.[1] I now know what you mean and must confess that you did not misunderstand me, after all: I did indeed hold the view that with a collision-broadening, constant A does in fact increase with a grow- ing number of collisions for the extinction coefficient, which you write as , in just the way that Lorentz calculated it classically. If I have un- derstood Minkowski correctly,[2] he finds in his experiments that, excluding for- eign gases and at an Na-vapor pressure below mm, A is constant and has ap- proximately the value that results from the classical theory of scattering at a higher vapor pressure for Na, however, A increases, whereby at the same time the frequen- cy-dependence of nκ no longer corresponds to the above formula, but nκ rather di- minishes more gradually, as the distance increases from , as proportional to . The influence of foreign gases is still being examined at the moment. With kind regards, yours sincerely, R. Ladenburg nκ A n n0)2 – ( --------------------- = 10 2– n0 1 n n0)2 – ( ---------------------