https://commons.wikimedia.org/wiki/File:S_long_serif_et_sans...
This is similar to the German 'ss' or 'sz' (one long 's' followed by a short 's') which when printed or written in the Gothic font looks like a Greek 'beta'.
https://graphicdesign.stackexchange.com/questions/68183/how-...
This makes reading the text extremely difficult and infuriating. Consider 'fubject' instead of 'subject', and 'whofe' instead of 'whose'. It's like I suddenly developed a lisp or something.
Just curious why the printer of that book may have used this typeface.
https://en.wikipedia.org/wiki/Long_s
Wikipedia has a long description of the history and how it went out of use. It's actually not quite identical to the letter f (it's ſ rather than f) and is also the original of the integral sign in calculus.