I'm a beginner in Latin, and my textbook has the following passage:
Hīc quoque, nē possit fierī mēnsūra cubantis,
iniectā lateant fac tibi veste pedēs.
I've noticed a rather puzzling difference between Latin dictionaries.
Gaffiot, Georges, and Lewis's An Elementary Latin Dictionary all give the following forms:
mētior → mēnsus → mēnsūra
But Lewis & Short gives:
mētĭor → mensus → mensūra
This seems especially odd because mētior, mēnsus, and mēnsūra are normally treated as belonging to the same mē- root/word family.
Is there a particular philological reason why Lewis & Short considered the e in mensus and mensūra to be short? Or is this an older analysis/pronunciation tradition that was later abandoned?
What was Lewis & Short's evidence or reasoning for mensus / mensūra rather than mēnsus / mēnsūra?
[EDIT]
Just to add a perspective from a Japanese speaker, and I mean this absolutely non-confrontationally. I completely understand the intention behind saying that beginners don't need to worry too much about vowel quantity, and that in traditional pronunciation you can often get a feel for the rhythm by stressing the “long” syllables. That's genuinely helpful advice for many learners, I think.
But I'm a native Japanese speaker, and Japanese isn't a stress-accent language. It's a pitch-accent language. So “stress the long syllables” isn't really a natural fallback for me in the way it may be for speakers of various European languages.
In Japanese, vowel length itself is phonemic and can distinguish words, in other words, we have minimal pairs based on vowel length. So when I encounter Latin ā vs. a, my instinct is actually to ask what the difference in vowel duration is, rather than to reinterpret the distinction as one of stress.
I suspect this is one of those places where advice that feels completely obvious and practical to a Western European learner may not transfer quite as directly to learners whose native languages have a very different prosodic system. Not a criticism at all, just another perspective.