Ryan was the first person to express "so" with symbols. In an algebra book 1659, he used symbols ∴ and \ to mean "so", of which ∴ was used more.

The English version of the book 1668 also uses these two symbols to mean "so", but "∵" is used more. Jones uses ∴ in 1706 to mean "so". By the middle of18th century, "∵" was used to mean "so", at least as much as "∴". "

By 1827, Euclid's Elements of Geometry published by Cambridge University used ⊙ for "because" and ∴ for "so" respectively. This usage has become more and more popular and has been used ever since.