D O C U M E N T 3 4 9 A U G U S T 1 9 2 6 3 4 7 that I proposed hardly satisfies me either.[7] It does not permit any singularity-free charged masses. Furthermore, I cannot make myself glue two things together (like the left- and right-hand sides of this equation) that have nothing to do with each other logico-mathematically.— I have now decided to go home tomorrow because I’ve been traveling around quite a long time already and I’m thirsting for rest and concentration. My wife no. 2 also needs some thorough moral support, as she is stuck all by herself with her hopelessly ill mother.[9] Warm regards to you and Anna[8] from your Albert 349. To Josepha Whitney-Newcomb[1] Berlin, 15 July [August] 1926[2] Dear Mrs. Whitney, I write with reference to our meeting in the building of the League of Nations and attempt to give you the information desired. Your father’s[3] lifework is of monumental importance in astronomy. It can be characterized as follows: Through empirical tests, Kepler discovered the laws ac- cording to which a planet would move around the Sun, provided there were no other planets besides it. From those laws, Newton derived the universal laws of mo- tion, as well as his law of gravitation. Newton’s laws state, in a wholly general way, what the movements of masses must be when the influence they exert upon one an- other is due to no other force than gravitation. When there are more than two bodies it becomes very difficult to calculate what motion takes place during a longer peri- od of time. In our solar system, the conditions are not so exceedingly difficult inasmuch as one of the bodies, the Sun, is greatly preponderant in mass. One obtains for a single planet a motion that differs only slightly from what it would be if only the planet in question and the Sun were to exist. If this were not so, Kepler could not have found his laws, and it is inconceivable how, in that case, the science of astronomy would have been developed. The problem remains, therefore, to find out what influence the rest of the planets have upon the movements of each separate planet in the solar system. This is the “perturbation problem” in astronomy, the solution of which has engaged the attention of the most prominent mathematicians and astronomers for the past hun- dred years. Your honored father was the last of the great masters whose reckonings concerning the solar system, in this regard, were made with scrupulous attention to detail.[4] This is such a gigantic task that there only exist very few who approach the solution of this problem with an independent and critical mind.