The long s (∫) has its roots in Roman cursive and was common in print in Europe from the 15th through the 18th centuries. It still appears in the German Eszett (ß), which is an ss ligature (a connected long s and short s) that was common in European printing before the 19th century. Language writer, Ben Zimmer, was once looking for the earliest references to the fabric seersucker and he discovered that his searches were hobbled by the problem of optical character recognition (OCR) programs mistaking the long ‘s’ for a ‘f’ in old texts. He searched instead for ‘feerfucker’ and discovered late 17th century references that predated the earliest citations in the Oxford English Dictionary. You can hear the tale on the Lexicon Valley podcast. Although they varied a bit from one language to the next, there were rules on where the ‘∫’ was placed in text. Confusing the ‘∫’ with the ‘f’ was apparently not a problem in the three hundred years in which the long ‘s’ was in common printed use.