From The Musar Movement by Rabbi Dov Katz (English translation), pp. 301-302 n. 2:
See S. Mark, op. cit., pp. 8890. The author also relates that Prof. Hermann Helmholtz, the famous philosopher and scientist, evinced an interest in meeting R. Israel, and an animated conversation took place between the two of them. Helmholtz seized the opportunity to express his surprise that the Talmud, which is built on such solid and logical foundations should have given space to such legends which sound like fanatical and outlandish fantasies, such as the stories of Rabbah bar bar Chana, which tell of a bird standing in the sea, with the water reaching up to its feet, and its head to heaven (Baba Batra 73b). R. Israel answered by using an analogy: They were living in 1871, after Germany had won its great victory over France. The King of Prussia had been crowned Kaiser of all Germany. His emblem was an eagle. Previously it had been one-headed; now it had become two-headed. Hundreds of poets and authors had celebrated the event in diverse forms. He himself had read a poem in which the author had given a description of the glory of modern Germany in these terms: The great German eagle had one head reaching out to Memel and the other to Metz; its one wing tip touched Kiel and the other Badensee. They knew the reference. The poet had described how far German territory now extended in all four directions. Now, the professor could imagine to himself that 600 years hence when no one would remember how Germany had been fragmentized in principalities and the metaphoric description of the rise of the monarchy someone would find a story of a two-headed eagle with wings extending some 300 miles in some library. Would he not express the same opinion as the professor had on the stories of Rabbah bar bar Chana? Obviously, just as they understood the import of the two-headed eagle, so did the people of those times understand the implications of those stories, which were certainly richer in content than the mere description of an eagle. It was because the present was so far removed from that epoch that the description seemed so absurd to them. Similar approaches had to be adopted towards the other Aggadot of the Talmud as well. The reply is characteristic for R. Israel, and shows his rationalistic bent.