But such diversity and beauty of things is available on the other planets like our Earthly realm, surely they wouldn't lack a spectator! As the elegance and artful workmanship of the animals, and the colors and scents of the flowers seem to be made available for human admiration and delight, will there not be beings on these planets who [could] enjoy so many and so pleasing spectacles? ["Quod si igitur similis quaedam rerum varietas ac pulchritudo in caeteris planetis atque in Terra hac nostra viget, nunquid spectatore carebunt! an non ut animalium elegantia et artificiosa fabrica, florum colores atque odores ad hominum admirationem aut voluptatem comparata videntur, ita et in istis existent aliqui qui tantis spectaculis tamque jucundis fruantur."--Christiaan Huygens (ca 1689).
In the first edition of Newton's Principia (1686), God is mentioned only once, deep into the technical details of Book 3: ''Therefore God placed the planet at different distances from the sun so that each one might, according to the degree of density, enjoy a greater or smaller amount of heat from the sun'' (Book 3, proposition 8, corollary 5; quoted from the Whitman/Cohen translation, p. 814). This claim was removed in subsequent editions of the Principia, and Newton moved his natural theology -- without this particular argument -- to the new conclusion of the Principia, his General Scholium.
At least one person discerned the significance of Newton's remark in Book 3 of the Principia. As Bernard Cohen argues in his (1690) Discourse on Gravity, Huygens comments on proposition 8 that it showed what kind of gravity ''the inhabitants of Jupiter and Saturn would feel,'' (quoted from Cohen's long introduction to the translation of the Principia p. 219). We know that Huygens had empirical reasons to doubt Newton's argument for the inverse-square law as a universal quality of matter, but Huygens certainly accepted an inverse-square rule for celestial gravity that governed the planets.
As an aside, despite the fact that the argument was removed after the first editions, Kant, who knew his Huygens, also saw Newton's point: ''Newton, who established the density of some planets by calculation, thought that the cause of this relationship set according to the distance was to be found in the appropriateness of God's choice and in the fundamental motives of His final purpose, since the planets closer to the sun must endure more solar heat and those further away are to manage with a lower level of heat,'' (UNH, Part 2, section 2, 284–85 (271)).
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