Definition:Integral Sign/Historical Note

Historical Note on Integral Sign
The integral sign $\displaystyle \int \ldots \ \mathrm d x$ originated with

In a manuscript dated $29$th October $1675$ he introduced a long letter $S$ to suggest the first letter of the word summa (Latin for sum).

At the time he was using the notation $\operatorname {omn} l$ (that is: omnes lineae, meaning all lines).

Then he noted:
 * It will be useful to write $\int$ for $\operatorname {omn}$, thus $\int \, l$ for $\operatorname {omn} l$, that is, the sum of those $l$'s.

At the same time he introduced the differential symbol $\mathrm d$.

Thus he was soon writing $\mathrm d x$, $\mathrm d y$, and $\int \ldots \mathrm d x$ soon followed.