Do you have plans to watch the eclipse today? I do! As you read this, imagine me already stationed within the path of totality.
If you are experiencing eclipse fever, you may be interested, like I was, to know what books we have in Special Collections related to eclipses. A quick search of the library’s catalog brought back the following book with the subject heading, “Solar eclipses — Mathematics”:
Petrus Elvius. Exercitium mathematicum eclipsiographiam solis leviter adumbrans… Upsaliæ : Literis Wernerianis, 1710. Call number: QB541 E48x 1710.
Checking the shelves I found a small pamphlet bound in blue paper wrappers that have become entirely detached. It is kept in this protective four-flap binder:
The title page begins with the line, “Auspice DEO!” (Under the auspices of God!). Although this was published early during the Age of Enlightenment, we can surmise that it took some time for the influence of religion on science to recede.
Written in Latin, the Eclipsographia solis, as it is also known, contains an explanation of the mathematical calculations of eclipses, including their duration. At the beginning, after the dedication, there is this delightful fold-out set of diagrams:
What did people know about eclipses, or even the solar system in general, when this pamphlet was published in 1710? People have been awed by–and therefore have studied–the phenomenon of eclipses for millennia. The astronomer Gerald Hawkins contended in the 1960s that Stonehenge was used to predict eclipses. Eclipses were studied by the ancient Babylonian, Chinese, Arabic, and Greek astronomers. Anthony Aveni writes in his book In the Shadow of the Moon, “Beginning about the sixteenth century, eclipse observations of a scientific nature begin to enter historical records on the European continent” (p. 137). In 1543, with the publication of his book De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres), Nicholas Copernicus revolutionized European astronomy by demonstrating mathematically that the Sun, rather than the Earth, was at the center of the universe. Galileo later defended the Copernican system in his 1632 publication Dialogo sopra i due massimi sistemi del mondo (Dialogue Concerning the Two Chief World Systems), which got him in trouble with Pope Urban VIII and led to his house arrest. Johannes Kepler improved on the work of Copernicus with his work on the laws of planetary motion, elucidated in his Astronomia nova (New Astronomy) published in 1609. Isaac Newton in 1687 published his Principia, in which he stated his laws of motion and universal gravitation. He also showed how Kepler’s laws followed the same principles as his law of gravity, proving that the same laws of motion govern objects both on the earth and in space.
It would seem by 1710, when our pamphlet was written, that European astronomers knew quite a bit about the solar system and the movement of the planets. In reality, it took some time for the new ideas about the solar system to be fully accepted. (Remember the “Auspice DEO!” of the title page?) Petrus Elvius, the author of our pamphlet, was a Swedish professor of astronomy at Uppsala University and lived from 1660 to 1718. According to his entry in the Swedish Biographical Dictionary (Svenskt biografiskt lexikon), his position on the Copernican system was not clear, and he expressed doubt over the validity of Newton’s law of universal gravitation in a letter 1711 letter to Emanuel Swedenborg, calling it “abstraction” and not physics.
Interestingly, this book was published 5 years before the May 3, 1715 total solar eclipse that crossed central England and Northern Europe. Edmond Halley, famous for calculating the orbit of the eponymously named Halley’s Comet, predicted the path of the eclipse with a very high degree of accuracy (within 4 minutes) and drew a map of its path across England. This map helped to promote popular interest in eclipse-watching (much like today), and it also set off a period of increasingly accurate eclipse mapping.
Happy eclipse day, everyone!
Aveni, Anthony. In the Shadow of the Moon: The Science, Magic, and Mystery of Solar Eclipses. Yale University Press, 2017.