The long “s”
Answer: This is what is known as a “long s”. It does look like an “f”, except that a “long s” does not have a horizontal crossbar on the right side. It can be credited to Guttenberg and the first generation of printers in Germany in the late 1400’s. When they invented movable type printing, they wanted the letters to look similar to fancy late Middle Age way of writing by hand. The thick font that they came up with is what we call today “Blackletter”, “Gothic”, or “Old English.” When in the early 1500’s, the simpler and more readable “Roman” and “Italic” fonts became popular, the “long-s” was still retained. The long-s was used all over Europe, the United States , and all over the Western world until the 1790’s.
A long-s is still pronounced the same way as the standard “short-s.” We know this because the capital letter of both a long-s and a short-s is the same standard “S.”
The long-s was used in place of a standard s, except for the following places: (1) at the end of a word, (2) before or after the letter “f”, and (3) before the letter “b”, and (4) before the letter “k.” Rules (3) and (4) are really suggestions, and differed according to the printer. Between 1750 and 1800, it was actually more common to see the long-s before the “b” and “k” than it was in earlier eras. In some rare cases, I have seen where in a pair, only the first “s” was long, and the second one was short. If a word is abbreviated, such as “Thessalonians” to “Thess.”, it was usually customary to retain the long-s before the period, but any other time the last “s” of a word was a short “s.”
I hope this was helpful.