March 4, 1955
In the beginning of March Einstein started again to visit the Institute; a call came from him through Miss Dukas: would we not come that evening?; he would like to discuss my letter.
Einstein was in his study, his feet wrapped in blankets, and an electric heater burning close by; he stood up in an attempt to bring us blankets too, though it was not cold in the room. A glass of water was on the table in front of him. I had not seen him since he became sick over a half year earlier. His face was rounder, his composure was mellower. He would not argue as vigorously as he usually did, and less often laughed his uproarious laugh.
He read my letter aloud, line after line, and discussed it; he read with great relish the page of Newtons that I includedthe very last page from the Principia, where Newton made a prophetic statement concerning the role of electricity in nature; and we discussed Newtons discoveries, and the discoveries of Kepler of the ellipticity of planetary orbits. Einstein read my explanation of gravitation as a dipole, but could not see how I explained inertia; of his own work he thought this was the greatest achievement, his stressing the equality of gravitational and inertial masses (I quoted de Sitter that Newton himself regarded this equality as a remarkable coincidence).
We succeeded to read only up to page 9 in my letterit became late, and although Einstein was prepared to go on reading and discussing, I asked to postpone this in order to spare him. Thus we interrupted the session after plan 2, at about 10:30, after two hours. At the end Einstein told me that I am not given to change of mind.
In general Einstein was on the defensiveinsofar as he had to deny many facts and explanations that are accepted in astronomy: he saw the consequence for celestial mechanics where the people who formulated the theories did not see them. In our discussion I mentioned for instance that the unusually high energy of cosmic rays is explained by the existence of magnetic fields in which, as in a cyclotron, charged particles are accelerated in the solar corona, whirled to very high energies. But if there is such a field, the earth, a magnet, must also experience an effect as it travels through itan argument that came to my mind on the way to Einsteins house that evening. Seeing this consequence, Einstein denied the existence of such a field; the other explanation, that cosmic rays achieve their energy because they are accelerated by a charged earth, certainly did not help him out of the difficulty: therefore he stated that we do not know what causes high energy cosmic rays. The circumstance that the sun rotates more quickly at the equator than at higher latitudes Einstein thought to explain possibly by some thermal effect. But the same phenomenon is observable on Jupiter, and he wondered that Jupiter is cold; could it not possibly be hot? Are not its satellites illuminated by it?
As to comets tails, Einstein expressed his disbelief in the high velocities achieved by the tails, and when I referred to John Herschel and W. Pickering, he wished to see the statements. After a few days I mailed these statements to him:
I cannot say differently: I became strongly attached to Einstein, as a son to a father, and I felt warmth coming in his feeling toward me. He said also that he too had almost everyone opposing him, but it is harder to tangle with them than with methey would go into mathematics.