In the old days, what we now call the ‘solution’ of a differential equation,
was used to be referred to as ‘integral’ of the differential equation, the word
being coined by James Bernoulli (1654 - 1705) in 1690 The word ‘solution was
first used by Joseph Louis Lagrange (1736 - 1813) in 1774, which was almost
hundred years since the birth of differential equations It was Jules Henri Poincare
(1854 - 1912) who strongly advocated the use of the word ‘solution’ and thus the
word ‘solution’ has found its deserved place in modern terminology The name of
the ‘method of separation of variables’ is due to John Bernoulli (1667 - 1748),
a younger brother of James Bernoulli