Simon Schaffer – Authorized Prophets: Comets and Astronomers after 1759

2 November, 2017 - MA Coursework

Simon Schaffer, “Authorized Prophets: Comets and Astronomers after 1759,” Studies in Eighteenth-Century Culture 17 (1987): 45-74.


Before Simon Schaffer’s 1987 “Authorized Prophets: Comets and Astronomers after 1759” Clifford Lecture, the historiography held fast to the conclusion that the comet of 1759 (a Halley’s), the long-awaited and predicted return of the comet of 1682, heralded the “triumph of a single form of rational astronomy” and “mark[ed] the destruction of cometary and cosmological significance.” In fact, even more simplistically, cometary theory was supposedly completed after the 1682 comet, and its 1758-9 return simply a reassuring spectacle. Schaffer’s lecture, with its focus on Jerome Lalande and Johann Lambert, seeks to contradict both these assertions and argues that the comet of 1759 “was a resource used for profoundly differing theological, ideological and cosmological purposes.” It goes without saying that the triumphalist historiographic consensus that inspired Schaffer’s resistance was predicated on the linear-progressionist (need I say whiggish) school of the history of science about which you have had to so often hear me complain, in which Halley, in concert with Newton, got it right, and in 1682 predicted the return of that year’s comet some ~75 years later (in the story we tell the public he predicted it exactly). Lo and behold the comet reappeared when Halley said it would.

But history is always more complicated than story, as Schaffer is keen to inform us. The reappearance of Halley’s comet in 1759 did not eliminate cometary cosmic significance, and its proof of celestial mechanics was not self-evident. In fact, Schaffer, as he was so fond of doing in the 1980s, insists that the triumph of celestial mechanics through the reappearance of the comet was “a deliberate task set by workers in London and Paris,” in other words artifice made possible in the context of a certain social milieu.

Much of that work was done by Jerome Lalande. In the years immediately prior to the expected return of the 1682 comet, Lalande, along with Clairaut and Mme. Lepaute began calculating the gravitational effects of Jupiter and Saturn on the comet. They determined that these pulls would delay the comet some 20 months (they would themselves be 30 days off). Without this adjustment, the predicted return could have passed for little more than coincidence, 20 months is hardly an encouraging degree of specificity for a supposedly regular and quantifiable mechanical process. With this adjustment, however, the precision of the calculation of the expected return becomes uncanny in its precision, and, furthermore, the comet is put to work overtime to serve as an impressive demonstration of the theory of universal gravitation — acknowledging the gravitational force of all bodies of mass, in this case Jupiter and Saturn. Lalande’s calculations of cometary delay stimulated still further research. Arguing against Euler’s hypothesis of a resistant aether, in an October 1757 paper Lalande pointed out that this conjecture would spell the eventual demise of the solar system as the planets would collapse into the Sun; this resistant aether, if it existed, like the gravitational pulls of Jupiter and Saturn would also have further delayed the transit of the returning comet. When the comet (roughly) arrived according to Lalande’s original calculations, there was no evidence for further deviation by resistant aether.

Of particular interest (and further evidence that the comet of 1759’s triumph was not self-evident), was the effort Lalande was required to exert in convincing his audiences that the comet of 1579 was the same as that of 1682. After all, it had rather different look in its return. Lalande was forced to spend a considerable portion of his re-edition of Halley’s Synopsis emphasizing the Newtonian explanation of comet tails — they had to be understood as constantly variable for the comet of 1579 to be identifiable with that of 1682. And still, to the casual natural-philosophical hobbyist with an iota of common sense, acknowledging that comet’s tails are constantly changing is not demonstrable proof that two differently-appearing comets are the same comet. This is of great interest to me: if the two comets were not recognized as one, the comet of 1759 confirms neither the periodicity of comets, nor Halley’s cometography, nor universal gravitation, nor denies the existence of Euler’s resistant aether. All of these “proofs,” to the pre-Schafferian historiography so indisputably indicative of a rationalist positive triumph, made possible by Lalande’s considerably elaborate quantitative gymnastics calculating the effects of Jupiter’s and Saturn’s gravity on the comet’s path, depend upon the qualitative judgment of the comet’s appearance. In contrast to the assumptions of our pre-1987 historiography, the work on cometary theory was far from over in 1759.

And likewise neither was cometary cosmic significance. Halley and Newton themselves acutely embody this contradiction. While their cometography was “rashly” assumed to put an end to this signification, they insisted comets “could fit into a single divinely planned economy” and connected them “with the stability of the solar system, the scriptural history of the Earth, including the Deluge and the Apocalypse and the restoration of matter and activity of the planets and the Sun.” These insistences gave post-Newtonian thinkers like Maupertuis and Wiston license to drum up cometary scenarios as eschatological as those of Reformation Protestant doomsayers, much to Johann Lambert’s frustration who quipped that “comets are no longer fearful through their significance but through their effect” and reduced his post-Newton contemporaries as “no better than what he called ‘authorized prophets.’” This diminutive moniker, I think, and I think Schaffer hints as much in his lecture, could just as well be applied to Newton and Halley, and, more imporantly, to the historians of science who told us bedtime stories of the inexorable triumph of reason over superstition, little aware of their infantile resemblance to Grimm moralizing about the triumph of Good over Evil, Light over Dark, and just about as mythological to boot.


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