About the surname Yos(h)ida

Question

I have recently bumped into the Japanese mathematician 吉田{よしだ}耕筰{こうさく}. I was wondering two things about his surname:

1. Why is it so often spelt Yosida instead of Yoshida? And taking lead from it, when did し change sound from /si/ to /ɕi/? That is, is it possible that at the time this mathematician was working his name was actually read /Josida/, hence the spelling? Or is it an older scheme of transliteration that stuck for some reason?
2. Where should I stress Yoshida? /'joɕida/, /jo'ɕida/ or /joɕi'da/? Naturally, the answer to this lies in the Japanese pitch accent, so how is the pitch accent of this particular word?

Answer 1

1. Spelling conventions are different. It's almost certainly not the case that the pronunciation has changed since then, as evidence suggests that /si/ has been [ɕi] since Old Japanese in the 700s (and also suggests that /se/ was once [ɕe], meaning that the overall direction might well be from [ɕ] to [s] rather than the other way around). Some romanisation systems (such as Hepburn) prefer to represent as accurate a pronunciation as can be conveyed in letters (hence ‹shi›); other systems prefer either internal regularity or 1:1 phoneme-to-letter correspondences (giving ‹si› to be consistent with ‹sa› etc). These days the most common system for names is some variant of Hepburn; this was not always the case in the past (which is likely why your mathematician's name isn't in proper Hepburn).

2. As for the accent, my (admittedly non-native) gut instinct suggests [jòɕídá] or [jòɕídà] and [kóòsàkù]. Others can correct me.

Answer 2

There is no /si/ in Japanese. /ɕi/ is the valid reading of し

し is romanized as SI and SHI, but it is always pronounced SHI (ɕi).

2. The stress I think comes naturally on the YO. YOsheeda. KOosaku.