The Day We Found the Universe - Marcia Bartusiak [25]
Thomas Wright's engraving of the Milky Way,
depicting it as a disk of stars (From Thomas Wright's
An Original Theory; or, New Hypothesis of the Universe, 1750)
Wright included a number of lush illustrations, thirty-two in all, which conveyed his seminal ideas better than the text itself. One engraving—the one still found in textbooks today—displays the Milky Way as a flat layer of stars. This was a first step in imagining his huge spherical shell. “I don't mean to affirm that [the disk] really is so in Fact,” he wrote, “but only state the Question thus, to help your Imagination to conceive more aptly what I would explain.” Looking along the plane of Wright's big, gently curving shell, in which the Sun is embedded, Earth's inhabitants would readily perceive a disklike structure. The Milky Way appears as a band, mused Wright, because we observe this thin layer of stars edge-on; when looking away from the plane, stargazers see fewer stars.
Wright went on to consider whether certain cloudy spots, then being observed in the heavens in greater numbers, might be additional creations, bordering upon us but “too remote for even our telescopes to reach,” countless spheres with many “Divine Centres.” He seemed to be echoing the Swedish philosopher Emanuel Swedenborg, who in 1734 also wondered if “there may be innumerable other spheres, and innumerable other heavens similar to those we behold, so many, indeed, and so mighty, that our own may be respectively only a point.”
If left there, Wright's imaginative ideas and dazzling illustrations would have likely generated hardly a footnote in astronomical history. He even reverted to a more medieval cosmic model, outrageous in its fires-of-hell imagery, some years later. But as British historian Michael Hoskin first pointed out, Wright managed to achieve a degree of acclaim when others widely disseminated what they thought he meant. A few months after the publication of An Original Theory, its key ideas were summarized in a Hamburg journal. The review selectively stressed Wright's concept of the Milky Way as a flat ring, rather than a sphere. This ring was compared to our solar system, with the stars moving around much like the planets circling the Sun. Inspired by this brief journal account, a young Prussian tutor in 1755 wrote his own book on the subject. Like Wright, he described the nebular patches in the nighttime sky as “just universes and, so to speak, Milky Ways… These higher universes are not without relation to one another, and by this mutual relationship they constitute again a still more immense system.” These words were virtually ignored until the author—Immanuel Kant—achieved fame as one of the world's great philosophers. Even then his ideas on the universe's design almost didn't survive. Kant's manuscript was destroyed when his printer went bankrupt. Fortunately, a shorter version was tucked away in the appendix of another book that he published in 1763.
Kant, trained in science, imagined that Wright's ring of stars was actually a continuous disk. This was more than wishful thinking; he was inspired by the latest astronomical evidence. Pierre-Louis de Maupertuis in France had been observing dim objects in the sky, what he called “nebulous stars,” that appeared elliptical in shape, the very way a disk would appear when tipped at an angle. “I easily persuaded myself,” wrote Kant, “that these stars can be nothing else than a mass of many fixed stars… On account of their feeble light, they are removed to an inconceivable distance from us.” With such reasoning, Kant arrived at the correct image of a galaxy's basic structure. Kant was astonished that previous observers of the heavens had not figured out the structure of our galaxy earlier. The Milky Way resembled a flat plate. Moreover, it was just one of many star-worlds scattered throughout the heavens. The German scientist Alexander von Humboldt later dubbed them Kant's “island universes,” a phrase