Whats is something that scientist strongly believed in long ago, that today we know is false?

A theory.

Explanation:

a theory is something not comproved. A theory is a supposition a respect of something that believe and  there are not scientific proof, actually, everybody, had a base of science about the facts, but the theory still not is a proof.  It's pass to be a true after of a proof.

faithful servants eumaeus and philaetius:

his ragged vest then drawn aside disclosed the sign conspicuous, and the scar exposed: eager they view'd, with joy they stood amazed with tearful eyes o'er all their master gazed:

these servants know ulysses by the scar he got when he was a child - so when he showed them the mark, they immediately knew this is truly their master and they hugged him, finally starting to believe his words.