Halley’s Reward

“I keep [a] subject constantly before me,” Newton once remarked, “and wait ’till
the first dawnings open slowly, by little and little, into a full and clear light.”
Kepler’s laws had been on Newton’s mind since his student days. In “first dawnings”
he had found connections between the inverse-square force law and Kepler’s
first and third laws, and now in De motu he was glimpsing in “a full and
clear light” the entire theoretical edifice that supported Kepler’s laws and other
astronomical observations. Once more, Newton’s work was “the passionate study
of a man obsessed.” His principal theme was the mathematical theory of universal
gravitation.
First, he revised and expanded De motu, still focusing on celestial mechanics,
and then aimed for a grander goal, a general dynamics, including terrestrial as
well as celestial phenomena. This went well beyond De motu, even in title. For
the final work, Newton chose the Latin title Philosophiae naturalis principia
mathematica (Mathematical Principles of Natural Philosophy), usually shortened
to the Principia.
When it finally emerged, the Principia comprised an introduction and three
books. The introduction contains definitions and Newton’s candidates for the
fundamental laws of motion. From these foundations, book 1 constructs extensive
and sophisticated mathematical equipment, and applies it to objects moving
without resistance—for example, in a vacuum. Book 2 treats motion in resisting
mediums—for example, in a liquid. And book 3 presents Newton’s cosmology,
his “system of the world.”
In a sense, Halley deserves as much credit for bringing the Principia into the
world as Newton does. His initial Cambridge visit reminded Newton of unfinished
business in celestial mechanics and prompted the writing of De motu.
When Halley saw De motu in November 1684, he recognized it for what it was,
the beginning of a revolution in the science of mechanics. Without wasting any
time, he returned to Cambridge with more encouragement. None was needed.
Newton was now in full pursuit of the new dynamics. “From August 1684 until
the spring of 1686,” Westfall writes, “[Newton’s] life [was] a virtual blank except
for the Principia.”
By April 1686, books 1 and 2 were completed, and Halley began a campaign
for their publication by the Royal Society. Somehow (possibly with Halley exceeding
his limited authority as clerk of the society), the members were persuaded
at a general meeting and a resolution was passed, ordering “that Mr.
Newton’s Philosophiae naturalis principia mathematica be printed forthwith.”
Halley was placed in charge of the publication.
Halley now had the Principia on the road to publication, but it was to be a
bumpy ride. First, Hooke made trouble. He believed that he had discovered the
inverse-square law of gravitation and wanted recognition from Newton. The acknowledgment,
if any, would appear in book 3, now nearing completion. Newton
refused to recognize Hooke’s priority, and threatened to suppress book 3. Halley
had not yet seen book 3, but he sensed that without it the Principia would be a
body without a head. “Sr I must now again beg you, not to let your resentment
run so high, as to deprive us of your third book,” he wrote to Newton. The
beheading was averted, and Halley’s diplomatic appeals may have been the decisive
factor.
In addition to his editorial duties, Halley was also called upon to subsidize the publication of the Principia. The Royal Society was close to bankruptcy and
unable even to pay Halley his clerk’s salary of fifty pounds. In his youth, Halley
had been wealthy, but by the 1680s he was supporting a family and his means
were reduced. The Principia was a gamble, and it carried some heavy financial
risks.
But finally, on July 5, 1687, Halley could write to Newton and announce that
“I have at length brought your Book to an end.” The first edition sold out quickly.
Halley at least recovered his costs, and more important, he received the acknowledgment
from Newton that he deserved: “In the publication of this work the
most acute and universally learned Mr Edmund Halley not only assisted me in
correcting the errors of the press and preparing the geometrical figures, but it
was through his solicitations that it came to be published.”