Halley's Quest A Selfless Genius and His Troubled Paramore (2005) / Chapter Skim
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12 Back to That Comet
12 Back to That Comet
Pages 168-180
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From page 168... ...
The memory of its cascade of seemingly burning light held his intrigue, its ephemeral passage replaying in his mind as if on its own peculiar orbit within Halley's skull. He hypothesized the comet not only orbited the Sun but that it was the same comet that had been seen earlier in the century.
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From page 169... ...
"I think there can be nothing plainer than that comets do move in orbs about the Sun [that approach the] parabolic." But the actual computations, which factor in the gravitational pull of not only Earth but also distant planets as the comet approaches, were highly complex.
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From page 170... ...
The chief difference between gravity and magnetism, we have since learned, is that while gravity only attracts, magnetism both attracts and repels. It was Halley who had initially persuaded Newton himself that the inverse square law of gravitation held true throughout the solar system.
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From page 171... ...
In 1717 he wrote that the differences between the orbits of 1531, 1607, and 1682 "seemed to me a little too large." He noted that the variations in the successive periods were "much larger than those which we observe in the revolutions of any single planet, since one of these periods exceeds the other by more than a year." He also noted that "the inclination of the comet of 1682 is 22 larger than that of the comet of 1607." In 1717, while plumbing medieval accounts, Halley found evidence of comets arriving before the Renaissance that might well be additional early sightings of the comet that reappeared in 1682. They had occurred on Easter 1305, an unspecified month in 1380, and in June 1456.
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From page 172... ...
Hooke's general theory put forward Earth as a dynamic, living body, one whose fertility changed over time. At his scheme's center were his ideas about the "Cause and Reason of the present Figure, Shape and Constitution of the Surface of the Body of the Earth, whether Sea or Land, as we now find it presented unto us under various and very irregular Forms and Fashions and constituted of very differing substances." Embracing his own theories on earthquakes, volcanoes, continent formation, magnetic variation, and even catastrophic changes in species, Hooke's new history of the natural world, in brief, linked celestial mechanics to Earth's dynamics.
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From page 173... ...
He doubted, however, whether the type of gradual flooding that would have occurred as a result of changes in Earth's rotational axis would have been extreme enough to wipe out entire species. Instead, Halley suggested in a 1686 paper that Earth's axis might undergo rapid shifts caused by "the powers that first impressed this whirling motion on the ball [Earth]
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From page 174... ...
"I have adventured to make these subterranean orbs capable of being inhabited," Halley added to the eternal pleasure of future science fiction writers. Perhaps amazingly, this notion of a hollow Earth still chimes with possibility today.While some scholars contend Halley borrowed from Hooke's earthquake lectures to develop his idea that Earth was comprised of shells, there is a stronger case to be made that his work was original and more directly stemmed from Newton's incorrect estimate of lunar mass.
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From page 175... ...
While much of Halley's radical thinking on magnetism would later fail to withstand scientific scrutiny, his ideas on comets would endure and he personally would remain devoted to the hypothesis on which he based his magnetic theory that Earth was comprised of shells. It was a premise that would help unlock the secrets of the aurora borealis -- those luminous clouds that form on the horizon, usu
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From page 176... ...
And in the past few decades the study of the solar wind or how charged particles move in the magnetic fields of celestial bodies, including Earth, has become a leading field of space research.) In 1724, after at last obtaining his dream job as England's second astronomer royal, Halley finally felt secure enough to publish his contentious paper written 30 years earlier.
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From page 177... ...
For example, in Newton disciple William Whiston's 1696 New Theory of the Earth, an early treatise based on Newton's Principia, he wrote that it was "now evident that gravity (the most mechanical affection of body) and which seems the most natural, depends entirely on the constant and efficacious and if you will the supernatural and miraculous influence of almighty God." But contemporary scholars contend that Newton was very much in support of Halley's idea that the current Earth with "visible marks of ruin upon it" had evolved from a previous one.
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From page 178... ...
P Loys de Cheseaux and even a Barbados plantation owner named Thomas Stevenson speculated that the irregularities in the periods were large enough that in fact two comets might be involved, each returning every 151 years.
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From page 179... ...
Before a mixed chorus of naysayers and believers in the public and the scientific community at large, the comet was sighted on Christmas Day 1758 -- 16 years after Halley's death.A well-to-do German farmer and amateur astronomer, Johann George Palitzch, documented its return above a little village near Dresden. Meanwhile in Paris, astronomer Charles Messier independently sighted the comet on January 21, 1759.
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From page 180... ...
Halley would be among the first to apply Newton's principle of universal gravitation and resulting laws to the physical realm. Perhaps a lot of that had to do with the reality that many natural philosophers of Halley's day didn't immediately buy into Newton's theory since it entailed such phenomena as unexplained action at a distance.
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