The language Isaac Newton invented
Newton is credited with many, many scientific innovations. His linguistic creations, on the other hand, never really took off.
Isaac Newton laid the foundations of modern science. He discovered gravity and the principles governing motion, light, and cooling. He invented a reflecting telescope, counterfeit-proof coins, and calculus. Most of his work made a huge and lasting contribution to the state of human knowledge, but a few of his projects never made it any further than the paper they were outlined on. All generations that came after him would benefit from his innovations, but none of them would ever speak his universal language.
When Newton was a young student just beginning college, he drew up plans for a language based on the nature of things, rather than on mere convention. The idea was to "let the names of the same sorte of things begin with the same letter: as of Instruments with s; Beasts with t; The soules passions with b, etc." In this way, words wouldn't just be arbitrary labels, haphazardly assigned. You could know from hearing a word what category of thing it belonged to. Additionally, prefixes and suffixes would indicate things like whether a word was a substance or an action, the actor or the acted upon, and so on. You could know, just by hearing a word, exactly what it meant.
This idea of a universal language where the words expressed their meaning through an orderly formula was in the air in the 17th century, and Newton was no doubt aware of the efforts that others had already made toward this end. There had been various plans published for languages based on symbols, numbers, or letters. Newton's plan was based on letters, and by varying the letters in a word, you could vary its meaning in a predictable way.
Newton's most fully worked-out example shows how prefixes could modify the meaning of tor (temperature) to produce all its related meanings:
owtor, exceeding hot
ǝwtor, very hot
awtor, pretty hot
ewtor, very little hot
iwtor, exceeding little hot
iytor, exceeding little cold
eytor, very little cold
aytor, indifferently cold
ǝytor, very cold
oytor, excessive cold
ator, neither very hot nor cold
ǝtor, pretty hot or pretty cold
otor, very hot or very cold
Newton tried to cram an awful lot into this one paradigm, and probably came to understand that if he wanted this degree of precision of meaning for every concept in the world, he would have to devote his life to this task. Instead, he moved on to other things. Another man of science, John Wilkins, a founding member of the Royal Society (of which Newton would later serve as president), did devote his life to the task, and would publish his own 600-page version of this type of universal language several years later. But that language, ingenious but impossible to use, quickly faded into obscurity. In deciding where to focus his energies and talent, Newton chose wisely.