I find quite interesting the choice for the shapes drawn into the sphere that resembles continents.
Was this choice arbitrary or do we know if there is some justification behind it?
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$\begingroup$ hmmm.... what continents do you think are shown here? $\endgroup$– Carl WitthoftCommented Aug 9, 2021 at 11:31
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$\begingroup$ No idea. But as the topic of Newton's cannon figure is about gravity I assumed that the sphere is meant to be a planet and the black spots would be landmarks. In any case, I don't know what they are and therefore the question. $\endgroup$– JonCommented Aug 9, 2021 at 12:14
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2 Answers
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It's very doubtful that the engraving/diagram had anything to do with Newton.
"The system of the world" was a posthumous publication from 1728-9 onwards. It was derived (with a little editorial amendment including a new title) from a manuscript of 1685 of Newton's (written out by his secretary/amanuensis but bearing corrections in Newton's hand). The ms is entitled 'De motu corporum Liber secundus'. Newton laid this aside in favour of a radical re-write that became Book 3 of 'Principia'. The superseded ms was found among his papers at his death.
I haven't looked exhaustively but I doubt if the diagram is with the ms, it was likely composed by someone else in preparation for publication, guided by the description in the text. So if the original even had a drawing, then it does not seem to have survived.
The original manuscript has been digitized and the page-images can be seen at
https://cudl.lib.cam.ac.uk/view/MS-ADD-03990/9 onwards.
A transcription is also online at the Newton Project, at https://www.newtonproject.ox.ac.uk/view/texts/diplomatic/NATP00305
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There seem to be alternative versions of this illustration: this one from page 6 of the Second Edition of On the System of the World [from the ResearchGate site]. I've always just taken this to be a "generic" planet for illustrative purposes. I've been looking for information on the engraver, in case anything was ever said about the intent of the image. It is supposed to be based on "the original sketch", but it wasn't clear if that is Newton's own.
For what it's worth, here's an example of a map Newton might have seen as a student. My own guess is that he may not have wanted to refer to Earth specifically, since he was describing what he took to be a "universal" result.
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$\begingroup$ As a matter of fact, I'd guess that Newton specifically avoided using an accurate depiction of the globe, since that would allow fixating on the specific launch point which could be derived from the illustration, and no end of quibbles might result. $\endgroup$ Commented Aug 17, 2021 at 16:09