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Theories on the Paths of Comets -- 

Nice example of Doppelmayr's Theoria Cometarum. . . , illustrating an array of different diagrams showing the theories of comets.

The image diagrams the theories of a number of the leading astronomers at the time, illustrating what would be the modern history of the paths of comets.  The principal models shown, those of Sir Isaac Newton, William Whiston and Edmund Halley, would revolutionize the science of comets and confirm Newton's theories on gravity.  

Prior to these theories, the prevailing theories involved something other than an elliptical path. Among the most current was the theory of Hevelius, which theorized an open ended parabolic path through the universe. Earlier theories such as Kepler viewed the paths as straight lines.  Relying upon Newton's theories gravity, Edmund Halley was the first to suggest that comets may be periodic, moving along very elongated ellipses rather than parabolic paths. He went so far as to forecast the return of the comet of 1680, which would become Halley's comet, with an estimated period of about 76 years, Halley expected the comet to be visible again between the years of 1758 and 1759. Halley died before he could view it with his own eyes, but others were able to test and confirm his conjecture and, with it, Newton's theory of gravity.

The models shown include those of:

  • Sir Isaac Newton / William Whiston / Edmund Halley
  • Johannes Kepler
  • Johannes Hevelius
  • Jean Dominique Cassini
  • Pierre Petite
  • Christiaan Huygens
  • Jean Picard

The primary theories shown are those of Newton and Whiston.  Whiston was an early advocate, along with Edmond Halley, of the periodicity of comets; he also held that comets were responsible for past catastrophes in Earth's history. In 1736, he caused widespread anxiety among London's citizens when he predicted the world would end on October 16,1736 because a comet would hit the earth. William Wake as Archbishop of Canterbury officially denied this prediction to calm the public.