I N T R O D U C T I O N T O V O L U M E 1 3 l x x i i i for water and ores (Vol. 7, 65a in the present volume), and another of a mechanism that produces reciprocating forward thrust, e.g., a power hammer (Doc. 18). The third one is more than a simple opinion. Two artists brought up the idea of a non- figurative film that uses freely drawn figures that change into other figures, an in- vention of one of the founders of the Dadaist movement, Hans Richter (Vol. 7, 52a in the present volume). Einstein was enthusiastic, looking on this proposal as a vi- sual counterpart to melody in music. A short remark on the independence of music from everyday experience (a rejection of descriptive music?) is an additional yield of this short note. Einstein also found time to think about smaller but interesting problems in phys- ics, such as the radiometer effect. He had previously chosen this problem for his cousin Edith Einstein’s doctoral dissertation, and it was obviously a topic that in- terested him beyond the mere need for him to find a tractable problem for a stu- dent’s benefit. He wrote a short manuscript in late 1922 (Doc. 339) that reported the main results of Edith’s thesis (Einstein, E. 1922), which itself had been con- ducted with many suggestions from Einstein (see Doc. 68). This manuscript re- mained unpublished, possibly because Edith did succeed in publishing her thesis (Einstein’s manuscript refers only to the dissertation, not to a publication), or be- cause Einstein had realized that the anisotropic pressure forces of the paper’s title were probably not sufficient to explain the radiometer effect as commonly under- stood. The following year he was to publish a paper in which he addressed what he thought was the origin of the radiometer effect at the usual pressures. IX With all its public attention and visibility, Einstein’s almost half-year-long trip abroad also afforded him long stretches of uninterrupted time for research. Entries in his diaries and comments in his travel correspondence testify to Einstein’s satis- faction about this opportunity to do some quiet thinking. For example, just after fin- ishing a manuscript about the unified field theory, he wrote to Bohr: “The voyage is splendid. I am enchanted with Japan and the Japanese and am sure that you would be, too. Moreover, such a sea voyage is a splendid existence for a ponderer anyway—like a monastery. Added to it is the caressing heat near the equator. Warm water drips lazily down from the sky and spreads peace and a plantlike dozing— this little letter testifies to it” (Doc. 421). Despite the various and many-sided interests that characterized Einstein’s activ- ities in Berlin, Leyden, or Kiel, the leisure time on board the ship gave him an op- portunity to think about issues that he cared about deeply and for which he needed