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By Root 540 0

and spent a good portion of his time just presenting basic astronomical facts: He carefully described the size of the Milky Way, its structure, and its constituent parts—the stars, gaseous nebulae, and clusters. He accompanied it with slides of the 100-inch telescope, the Moon, the Sun, the Pleiades cluster of stars, globular clusters. It was a visual tour of the known universe, with special attention paid to making the audience understand the meaning of a light-year. “You do not see the sun where it is, but where it was eight minutes ago,” he instructed. “You do not see these stars as they are now, but more probably as they were when King Cheops was a little boy.”

Instead of talking about the nature of the spiral nebulae, the very reason for the encounter, Shapley focused on his Big Galaxy model. He figured that if he proved the Milky Way was immense, the spiral nebulae would automatically be relegated to minor status in the cosmic scheme of things, mere hangers-on. Anticipating that Curtis would challenge his use of the Cepheids as standard candles in determining the globular cluster distances, Shapley simply ignored the technique in his remarks. “[Curtis] may question the sufficiency of the data or the accuracy of the methods of using it,” he said. “But this fact remains: we could discard the Cepheids altogether, use instead the thousands of B-type stars upon which the most capable stellar astronomers have worked for years, and derive just the same distance [to the globular clusters]…and obtain consequently the same dimensions for the galactic system.” But Shapley was being disingenuous. Two years earlier he had reported to the Astronomical Society of the Pacific that the Cepheids carried “so much greater weight” for his distance measurements and that the magnitudes of red giants and blue stars “can best be used as checks or as secondary standards.”

Shapley went on to stress his finding that the Sun is not at the center of the Milky Way: “We have been victimized by the chance position of the sun near the center of a subordinate system [of stars], and misled by the consequent phenomena, to think that we are God's own appointed, right in the thick of things.” As for the spirals? “I shall leave the description and discussion of this debatable question to Professor Curtis,” he said. Shapley conceded that the possibility remained that they were comparable galactic systems, but only if the Milky Way were cut down to a tenth of his newly defined dimensions. He believed that unlikely and preferred to think of the spirals as nebulous objects. He maintained “that it is professionally and scientifically unwise to take any very positive view in the matter just now.”

One can imagine Curtis's mounting dismay as his opponent was progressing through his talk. Shapley had spent most of his time on just the basics of astronomy, while Curtis had prepared a full-fledged analysis, laden with scientific detail. The Lick astronomer was about to address the audience on issues that Shapley had never brought up. While he anxiously awaited his turn at the podium, his mind raced, wondering whether he should change his approach on the fly, making his presentation more relaxed and general. But in the end he decided to stick to his original plan.

Unlike with Shapley, a copy of Curtis's script no longer exists, but some of his slides, displaying his essential points, do survive, and they provide a glimpse of the flow of his arguments that evening. Contrasting sharply with Shapley's popular approach to the topic, Curtis's talk was more technical, although by all accounts he spoke more spontaneously. At first he focused on one of his major disagreements with Shapley: the size of the Milky Way. He carefully outlined his reasons for believing that the Milky Way was a tenth the size that Shapley was hawking. Mainly, he had no confidence in Shapley's use of the Cepheids. Shapley himself knew that his momentous refashioning of the Milky Way's size stood on the foundation of eleven “miserable” Cepheids, as he had earlier described them in a letter.

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