In point of fact, Isaac Newton did not “explain just gravity”—he also invented the calculus and developed important insights into the nature of light, among numerous other contributions to science.
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Of course, this might not impact upon the point you are trying to make—you might just have selected a poor example.
However, casting about for a better example (immediately recognisable names who have made a singular contribution to science but did nothing else of note/had no significant, tangential side interests)...
Eliezer was not trying to give examples of people who made singular contributions but did nothing else. Rather, he was trying to give examples of singular contributions that had a lot to say about some things, but nothing of note to say about other things. His example was not Isaac Newton, but rather Newton’s theory of gravity.
In formulating his physical theories, Newton developed and used mathematical methods now included in the field of calculus. But the language of calculus as we know it was largely absent from the Principia; Newton gave many of his proofs in a geometric form of infinitesimal calculus, based on limits of ratios of vanishing small geometric quantities.
Eliezer was not trying to give examples of people who made singular contributions but did nothing else. Rather, he was trying to give examples of singular contributions that had a lot to say about some things, but nothing of note to say about other things. His example was not Isaac Newton, but rather Newton’s theory of gravity.
Inventing calclus could be said to be an integral element of Newton inventing his theory of gravity.
I see what you did there.
But seriously, the role of calculus is kinda interesting because he did it all geometrically, apparently: http://en.wikipedia.org/wiki/Philosophi%C3%A6_Naturalis_Principia_Mathematica