Astronomy and astrotheology

A number of Wright's ''schemes,'' as he called his illustrations, served as the basis for didactic works on astronomy, including The Universal Vicissitude of Seasons, articles about comets in the

Gentleman's Magazine, and diagrams explaining the appearance of lunar and solar eclipses. These broadsides would have made impressive visual aids for a lecturer, and are works of art in their own right.

In 1742, he finished a set of four plates, each 2 feet by 3 feet, illustrating a large number of basic astronomical phenomena. One of them shows, in the center foreground, the solar system—including not only the Sun and planets, but also many comets, and moons of Jupiter and other planets. In the corners of the plate, as background to the current conception of the solar system, he represented the Pythagorean, Ptolemaic, and other historical systems. The top of the plate bears a depiction of the Sun, and the bottom a map of the Moon.34

The set of four plates formed the basis of an elementary astronomy textbook. The full title of the work indicates that the text was merely the key (Latin ''clavis'') to the diagram: Clavis Coelestis, Being the Explication of a Diagram entituled a Synopsis of the Universe: or, the Visible World Epitomized. Although Wright's illustrations are striking, the content of the work is mostly conventional. The Clavis Coelestis treats ''plainly and simply,'' as its author says, of the planets, laws of motion, properties of light, the cause of seasons, calendars, tides, and the phenomena of eclipses and occultations. On the subject of a plurality of worlds, Wright is succinct. He says simply that all modern astronomers consider the stars to be ''great Globes of Fire like the sun,'' and that they ''may very possibly be the Centers of other Systems of Planets like ours, since we have no Reason that can contradict it, and many that may induce us to believe it.''35

One unusual aspect of Wright's overview of the solar system in Clavis Coelestis reminds us that he always had effects of geometrical perspective in mind. He not only gives the basic astronomical data on each of the planets—such as orbital period and distance from the Sun—but also conjures up for his readers what the view of the night sky would be from another location. He notes for example that ''To Mercury, the Sun and Venus are the only two great Bodies of the Universe. He views Venus and all the rest of the Planets, as we do Saturn, Jupiter and Mars; but Venus shines upon him with great Lustre, and 'tis probable, her great Light in opposition to the Sun, serves him instead of a Moon.''36

After the publication in 1742 of his Clavis Coelestis and accompanying diagram, and an account of a comet which he furnished to the Gentleman's Magazine, Wright's interest in astronomy per se appears to have waned. His situation was secure enough that he refused an offer that same year to become ''Chief Professor of Navigation'' at the Imperial Academy of St. Petersburg. He continued to teach, draw, and survey, but he also found time for touristic travel to sites such as Stonehenge and the garden at Moor Park.

In 1746, a trip to Ireland shifted the main focus of his enthusiasms to antiquities, the relics and monuments from the Stone Age to medieval times. He stayed in Ireland for several months as a guest of Lord Limerick, Governor of County Louth, and Bishop O'Gallagher of Raphoe, a town in County Donegal just a few miles from the prehistoric Beltony stone circle. Wright had a gift for sketching ''on the spot'' both the perspective views and cross-section plans of the castles and remains that he saw (see figure 3.4 for an example of such a combination drawing, made on a different tour, in England). Upon his return to London in the summer of 1747, he began preparing what was to be his most popular work in his lifetime: Louthiana, published in 1748, a description of the antiquities of County Louth. A second edition of this successful work was to follow in 1758.

Only after the success of Louthiana did Wright publish his astro-theological theory—or rather, a revised version of it—in the Original Theory of 1750. His journal entries end with the Irish tour, so we have no information on his activities immediately leading up to the publication of the Original Theory. What is clear is that something prompted Wright to ponder the Milky Way, and to try to reconcile this apparent ring of light circling the celestial sphere with his conviction that the stars of all creation orbit a divine center. Thinking like a clockmaker, a surveyor, and an architect, he kept turning the problem over in his mind: what does the appearance of the night sky, and in particular the swath of densely clustered stars in the Milky Way, say about the structure of the universe? In the Original Theory, he finally arrived at a world view that included the important elements of his astro-theological theory of the 1730s, but that also accounted for the appearance of the Milky Way based on geometrical arguments.

Figure 3.4 Wright perspective and plan drawings. Wright's artistic talent is evident in sketches and plans he made ''on the spot'' on tours of historic sites in England and Wales. (Reproduced with permission from the British Library.)

He wrote of his motivation: ''This luminous Circle has often engrossed my Thoughts, and of late has taken up all my idle Hours; and I am now in great Hopes I have not only at last found out the real Cause of it, but also by the same Hypothesis, which solves this Appearance, shall be able to demonstrate a much more rational Theory of the Creation than hitherto has been any where advanced.''37

The Original Theory takes the form of nine letters addressed to an unnamed friend, and a preface addressed to the public in which Wright begs ''every kind of Indulgence'' for offering a work ''entirely upon a new Plan.''38 Wright is conscious of breaking new ground merely by considering the problem of the Milky Way. He notes with justification that ''this amazing Phaenomenon which have been the Occasion of so many Fables, idle Romances, and ridiculous Opinions amongst the Antients, still continues to be unaccounted for, and even in an Age vain enough to boast Astronomy in its utmost Perfection.''39 Indeed, one of the mysteries of the history of astronomy is how astronomers from Ptolemy to Aristotle to Galileo could have given the Milky Way what one historian has called the ''silent treatment.'' Ptolemy contented himself with a description of the Milky Way and its location in the sky; Aristotle gave a patently unsatisfactory explanation of it as a kind of fog. Even Galileo, who saw it through a telescope and found it to be nothing but a congeries of stars, had nothing more to say about this unique clustering phenomenon.

Wright approaches the solution to this long-dormant problem slowly, guiding his reader through a number of concepts vital to an understanding of his hypothesis. His solution—his ''original theory'' — is based on the spherically symmetric universe that he conceived of in the 1730s, but this of course was his private rumination, not generally known. Thus the first letter seeks merely to convince his friend that the idea of a multitude of suns and planetary systems is not far-fetched or controversial. ''[T]hat the Stars are all Suns, and surrounded with planetary Bodies . . . is not a Thing merely taken for granted, but has ever been the concurrent Notion of the Learned of all Nations,'' Wright says.40 He quotes Newton and Derham, the author of Astro-Theology, among other astronomer-philosophers, to emphasize that a Creator whose power and wisdom are without bounds may very likely create multiple systems. His interlocutor appears to have had some difficulty accepting this premise, for Wright was obliged to revisit the problem. Letter the Fourth begins, ''Sir, You tell me you begin to be a tolerable good Copernican, and would now be glad to have my Opinion further upon the Nature of the Sun and Stars, with regard to the Suggestion of their being like Bodies of Fire. This you say will go a great Way towards confirming you in the Notion you have begun to embrace of a Plurality of Systems, and a much greater Multiplicity of Worlds than our little solar System can admit of.''41 If nothing else, this repetition of themes reminds us that the opinions of ''professional'' astronomers in Wright's day did not necessarily carry much weight with the general public, and that Wright was more mindful of this public than of astronomers who might be reading his work. Wright's style, too, shows that he was tailoring his arguments to the poets and philosophers among his friends. In contrast to the Clavis Coelestis, which is written very straightforwardly and concisely, the Original Theory is rife with literary quotations.

In Letter the Second, Wright addresses his friend's concern for method. The ideas of the Original Theory will not stand up to purely mathematical arguments or ''infallible Demonstration,'' Wright admits, but he intends to make use of analogy as an alternative, if weaker, way of reasoning. In particular, Wright attempts to convince his friend and reader that when spherical symmetry prevails in a system, it is possible to infer facts about the whole system from only a partial view. ''[F]rom a very small part of orbicular Things, we are able to determine the Form and Direction of the Whole,'' Wright notes.42

By way of introduction to the science, Letter the Third lays out the ''now-established Astronomy of Copernicus.''43 Wright reviews the principal facts about the planets — their orbital parameters, and their relative sizes — in the Sun-centered system and describes the trajectories of comets. This information is not critical to an understanding of his explanation of the Milky Way, except perhaps in the fact that the comets, with their orbits taking them far out of the plane of the solar system, provide a kind of precendent for assuming that the stars may have similar orbits about the divine center, as Wright imagined in his 1730s hypothesis. Letter the Fourth, as we have noted, returns to the arguments for the stars as suns with their own planetary systems, all at very great distances.

The fifth and sixth letters discuss the Milky Way, laying the groundwork for Wright's main hypothesis, which is contained in Letter the Seventh. Wright reminds his reader that the Milky Way circles the celestial sphere, nearly bisecting it, and that it is ''very irregular in Breadth and Brightness, and in many Places divided into double Streams''44 (see chapter 2). He recalls the fanciful explanations of this zone of light given by ancient peoples: it represents the soldering of the two hemispheres of the sky, or ''Juno's Milk, spilt whilst giving Suck to Hercules,'' or the track of Phaeton's wild ride with the chariot of the Sun.45

That the Milky Way actually consists of a large number of ''small'' or distant stars, Wright can argue from his own observations with ''a very good Reflector'' telescope.46 The light from these stars crowding together in the distance, Wright says, is combined; the rays of light coalesce so that the overall effect is like a river of milk. This phenomenon is repeated on a smaller scale in a number of nebulae, which, Wright asserts, are known to consist of stars. He mentions for example the nebula we now call the Beehive Cluster in the constellation Cancer, an open cluster which he believed contained 36 stars, and which we now suspect contains more than 200. He also quite properly lists the southern hemisphere's Magellanic Clouds, which he himself had never observed, as examples of cloudy regions consisting of many stars close together.

To give some idea of the distances of the stars, Wright invokes an experiment by the seventeenth-century astronomer Christiaan Huygens. Huygens had compared the brightness of the Sun and Sirius by covering his telescope, while it was pointed at the Sun, and allowing the light to enter only through a small hole. Judging from the amount by which he had to reduce the light from the Sun for it to appear comparable to the light from Sirius, and knowing how light diminishes with distance from the source, he inferred that Sirius must be at least 2 trillion miles away. Wright admits that these figures boggle the mind; he notes in connection with this that ''few People can range their Ideas with such Perspicuity, as to arrive at any adequate Notion of any Number above a thousand.''47

In Letter the Sixth, Wright asks his reader to grant him one postulate: ''That all the stars are, or may be, in fact, no less an authority than Halley provides the evidence that this is so. Wright quotes from Halley's paper in which the astronomer announces the discovery of what we now call the proper motion of stars. As mentioned earlier, Halley had been studying the star catalogs of Hipparchus as transcribed by Ptolemy, and had noticed that three stars — Aldebaran, Sirius, and Arcturus — had shifted their positions by more than half a degree in the intervening centuries. These shifts could not be accounted for by inaccuracies in observation, errors in transcription, or systematic changes in the positions of all stars due to a wobble in the Earth's spin axis. For Wright, as for many astronomers, the news suggested that all stars move. Only the nearest could be seen to move appreciably over the time span of human observation. Wright incorporated this astronomical fact in envisioning the stars as in orbit around a divine center.

Throughout these preliminaries Wright has hinted that the apparent lack of order and symmetry in the distribution of stars is the effect of our geometric perspective, and that from another location, we might view the disposition of the stars as orderly. In Letter the Seventh he states this explicitly. As viewed from the Earth's off-center or eccentric position in the solar system, he reminds his reader, the orbits of the planets are complex and their motions appear irregular. When viewed from the perspective of the Sun, at the center of the system, the planets are seen to move in relatively simple, orderly paths. Similarly, he says, ''nothing but a like eccentric Position of the Stars could any way produce such an apparently promiscuous [i.e., disorderly or random] Difference in such otherwise regular Bodies.'' There may be ''one Place in the Universe,'' Wright suggests, from which the order and motions of the stars appears ''most regular and most beautiful.''49 The favored perspective belongs, of course, to the divine center of a spherical universe. The illustrations to Letter the Seventh show a universe much like that he had described in the 1730s, with a divine presence at the center, surrounded by a spherical shell of stars orbiting in all directions.

The explanation for the Milky Way, the very heart of Wright's original theory, emerges from a consideration of the view from within the shell of stars. To drive home his point, Wright draws a close-up view of the shell of stars, showing a star such as the Sun near the middle of its thickness (see figure 3.5). Because the shell's thickness is small compared to the

Figure 3.5 The slab of stars, Wright's most famous illustration. The slab represents a close-up view of a small section of the entire system shown in figure 3.6. The slab, in other words, is a section of a thin shell which lies at a great distance from the divine center of the ''creation.'' (Reproduced with permission from Hoskin (1971).)

Figure 3.5 The slab of stars, Wright's most famous illustration. The slab represents a close-up view of a small section of the entire system shown in figure 3.6. The slab, in other words, is a section of a thin shell which lies at a great distance from the divine center of the ''creation.'' (Reproduced with permission from Hoskin (1971).)

radius of the sphere it defines, the curvature of the shell is barely perceptible, and the close-up view is a flat segment, with two parallel lines delineating the inner and outer surfaces of the shell. This close-up view looks very much like a slab of stars and, based on this diagram, later generations of astronomers sometimes mis-attributed to Wright the first modern conception of the Milky Way galaxy as a flat disk. However, it is clear from the text that Wright intended the slab to represent a small section of the ''orbicular'' or spherical system he had in mind.

Imagine the stars scattered about and filling the space in this segment, Wright asks his reader: ''consider what the Consequence would be to an Eye situated near the Center Point, or any where about the middle Plane, as at the Point A'' (in our figure 3.5). An observer would see the stars ''promiscuously dispersed on each Side, and more and more inclining to Disorder, as the Observer would advance his Station towards either Surface, and nearer to B or C.''50 That is, if the Sun and Earth were in the shell, but near the surface at B, the distribution of stars would be very uneven, with most lying in one hemisphere. If the Sun were near the middle of the starry region, all parts of the sky would contain stars.

Looking into the shell, on a tangent to the great sphere surrounding the divine center or in the direction of H or D, the observer would see the effect of innumerable stars extending to a great distance. Another of Wright's illustrations (see figure 3.6) shows the entire system from which the cross section was taken, and lines AD and AE, showing the direction in which the Milky Way would be seen. (In this figure, Wright has chosen to show two concentric shells of stars about the divine center, or what he calls ''a Creation of a double Construction.''51 Since an observer near the Sun sees only a limited region of his own shell of stars, indicated by the circle at G in the upper panel of our figure 3.6, there is no observational constraint to having more than one shell of stars.) In one long sentence, Wright summarizes the effect of the crowding of stars as seen from an observer at A: ''Thus, all their Rays at last so near uniting, must meeting in the Eye appear, as almost, in Contact, and form a perfect Zone of Light; this I take to be the real Case, and the true Nature of our Milky Way, and all the Irregularity we observe in it at the Earth, I judge to be intirely owing to our Sun's Position in this great Firmament, and may easily be solved by his Excentricity, and the Diversity of Motion that may naturally be conceived amongst the Stars themselves, which may here and there, in different Parts of the Heavens, occasion a cloudy Knot of Stars, as perhaps at E.''52 In other words, the irregularity of the distribution

Figure 3.6 Two views of spherical ''creation.'' (Reproduced with permission from Hoskin (1971).)

of stars in the sky, with a large number aggregated in the zone we call the Milky Way, is the effect of our immersion in the shell, which puts us in an eccentric position; viewed from the divine center of the system, the distribution of stars is actually regular and symmetric. Furthermore, as viewed from the Earth, the chance alignment of a number of stars as they pursue their separate orbits in the shell, around the divine center, may give rise to the appearance of a nebula or star cluster.

Wright is evidently highly pleased with this elegant and genuinely original solution to the problem. But he has to admit that the same logic would apply to an alternative distribution of stars about the divine center, one with the symmetry of a ring rather than a thin spherical shell. The phenomenon of the Milky Way may equally be accounted for, he notes, if the stars are arranged ''in the Manner of Saturn's Rings.''53 Figure 3.7 shows a top view of such a system, with the extent of the visible creation from an Earth-like planet limited to a shaded area. Indeed, if more than one creation is allowed, Wright is inclined to believe that there may be various systems of stars, some arranged spherically and some in rings about their respective divine centers. But it is clearly the spherical system that he prefers, and dwells on.

In Letter the Eighth, Wright tries to give his friend, to whom the letters were originally written, some idea of the scale of the solar system; apparently the friend had wondered why the Earth was not shown explicitly in Wright's schemes of the entire creation. Wright answers that if the Sun were represented by the dome of St. Paul's church, a sphere 18 inches in diameter in the West End neighborhood of Marylebone could stand in for the Earth, and a globe of about 12 feet diameter in the town of Chelmsford, some 50 miles from London, for Saturn, the last known planet. But, Wright notes, ''if you will take into your Idea one of the nearest Stars; instead of the Dome of St. Paul's, you must suppose the Sun to be represented by the gilt Ball on top of it, and then will another such upon the top of St. Peter's at Rome represent one of the nearest Stars.''54 Thus in drawing up his general scheme of the universe, Wright says, he judged the seat of the Earth to be ''of very little Consequence.''55

In the concluding Letter the Ninth, Wright returns to the idea of a multitude of worlds. From our perspective in the twenty-first

Figure 3.7 An alternative ''creation'' imagined by Wright; the stars lie not in a spherical shell, but in one or more rings around the divine center. (Reproduced with permission from Hoskin (1971).)

century, one of his more interesting speculations is that ''the many cloudy Spots'' in which ''no one Star or particular constituent Body can possibly be distinguished'' are ''external Creations, bordering upon the known Creation,'' or, if we can be permitted to equate his creations with stellar systems, other galaxies.56

The rest of Letter the Ninth is given to a consideration of the moral aspects of his hypothesis. The contrast with the more straightforward account of the spherical structure of creation is a bit jarring, but it serves to remind us that Wright's purpose was to integrate a physical and moral view of the universe. In the focus or center of Creation he sees a primitive fountain, overflowing with divine Grace, and it is here that ''the virtues of the meritorious are at last rewarded and received into the full Possession of every Happiness, and to perfect joy.'' The ideal worlds that Wright imagines have been created for the reward of the meritorious bear a striking resemblance to the magnificent ''naturalistic'' gardens he surveyed and helped plan among his friends in the aristocracy; he sees worlds ''fill'd with Grottoes and romantick Caves,'' and others ''with vast extensive Lawns and Vistoes, bounded with perpetual Greens, and interspersed with Groves and Wildernesses, full of all Varieties of Fruits and Flowers.''57

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