In Europe, two key mathematicians – Isaac Newton and Gottfried Leibniz – were competing for dominance regarding who was the inventor of Calculus. In the late 17th century, Bernoulli, a friend of Leibniz, attempted to challenge the mathematicians around the world to solve two complex problems based on Calculus.
In a letter from Leibniz to Bernoulli, Leibniz had stated that it would take him more than six months to solve the problem and asked for an extension.
Meanwhile, in England, Newton is known to have solved both the problems in a short span of 12 hours after he received Bernoulli’s challenge. Even though both mathematicians solved the problems, Newton had his work published anonymously as he suspected that it was all a ploy by Leibniz’s defenders. When Bernoulli announced the winners of the contest, he named Leibniz, l’Hopital and recognized Newton’s contribution publicly with the sentence
“tanquam ex ungue leonem,” Latin for “we know the lion by his claw.”
Bernoulli wrote the expression not publicly, but in a letter to Basnage de Beauval in March 1697, referring to the anonymous solution. The letter in French had ‘ex ungue Leonem’ preceded by the French word ‘comme’. The much quoted version ‘tanquam ex ungue Leonem’ is due to David Brewster’s book on the life and works of Newton in 1855. The expression comes from an ancient Greek sculptor’s claimed ability to tell the size of a lion from its severed paw. The intended meaning was that Bernoulli could tell the solution was Newton’s just as given a claw (or paw) it was possible to tell the animal was a lion. This was not meant to suggest any of the regarded superior qualities of the lion applied to Newton, as is often assumed.
This information was taken from The Mathematical Works of Isaac Newton Vol 8, by D. T. Whiteside, Page 9, Footnote 21