EINSTEIN, ALBERT. Autograph letter signed ("Papa") to Hans Albert Einstein, Princeton, 15 November 1936. 2 pages, 4to, 277 x 215 mm. (10¾ x 8½ in.).
SCIENTIST TO SON: "A PROBLEM FOR A REALLY GOOD MATHEMATICIAN"
"I have looked at your work and I admire your energy. You certainly have a scientific streak, and it is a pity we can't work on the major problems together. I will send your work to Karman [at the California Institute of Technology] and try to get him to take an interest in you. It is, however, very difficult to get a footing here, as I have learned in many cases, when I have tried to help young scientists. There seems to be an excess of scientific work, but for most of these positions, the pay is miserable. One of the difficulties in your case is, naturally, that it is more difficult for me to intercede on my son's behalf than for other people. Here, people are quite sensitive on that point." Einstein then turns to a consideration of his son's scientific work on the movement of sediment in water: "The nice thing about your work is that you are not taking as a constant the path between two fixed places, but instead define it through a law of probability [Einstein adds the equation here], which makes it possible for the first time to apply it to smaller units of time. I have now figured out how one could systematically tackle your problem, without leaving out the factor of the time in which the stone is in movement. I've arrived at the following." Einstein goes on to define the variables (which include time, place, the speed at which the gravel is moving, etc.) then sets up an equation for the calculation. He discusses certain variables which also affect the movement of the suspended particles and their expression in the equation. But, he adds, "the integration of the equation is, however, a problem for a really good mathematician." In a postscript he notes that he has "saved" the Zurich house for Hans Albert, although "when I'm not here anymore, it will be difficult for you, and I'm nearly 58."