R: The 1800' printing Long-s

The long, medial, or descending s (ſ) is a form of the minuscule (lower-case) letter s, which was formerly used where s occurred in the middle or at the beginning of a word (e.g. "ſinfulneſs" for "sinfulness" and "ſucceſsful" for "successful"). The modern letterform was called the terminal, round, or short s.

Something you will often see in old books we share.

Ref. https://en.wikipedia.org/wiki/Long_s