Is there a reason to expect an "old English expression"? At any rate,
the French expression must be extraordinarily rare, since, as others will have noted, it is not found much more than once by Google:
"que déjà convaincu par les yeux, il admît aussitôt ce qu'entendaient ses oreilles" - which the French translator [2nd edn, 1852?] of Tertullian, De Resurrectione, uses for T's "quo facilius credas prophetiae discipulus ante naturae, quo statim admittas cum audieris quod ubique iam videris", whereas the English translator followed T. closely: "you... might at once assent on hearing what you had already everywhere seen"

Sounds better to me this way round...

OR:
Having seen it with his/her very own eyes,...

The 'it' might need changing, depending on what it refers back to; it might, for example, read better as 'this', or several other possibilities..

--------------------------------------------------
Note added at 1 day 1 hr 51 mins (2004-05-14 22:02:33 GMT)
--------------------------------------------------

I\'m not entirely sure I understand your query, Jane. You have clearly interpreted \'what has been seen\' as being the person speaking, and indeed, if that is the case, then your version would certainly work a lot better than mine! However, I\'d like to understand just WHAT clues in the given context lead you to this conclusion? \'seen\' need not necessarily imply \'met me\', surely? Certainly, my first reaction on reading it was the idea that \'His Excellency\' [presumably NOT a real dignitary, just being very polite, as in olden times] has now seen \'something else\' that will lead him or her to effect the necessary introduction...

that's what it means for heaven's sake...the other answers are very awkward...

Now that you have MET ME.....ideas, ideas not words!!

--------------------------------------------------
Note added at 20 hrs 37 mins (2004-05-14 16:48:47 GMT)
--------------------------------------------------

OK...OLD ENGLISH

HAVING LAIDE YOUR EYES ON ME,

--------------------------------------------------
Note added at 20 hrs 38 mins (2004-05-14 16:49:28 GMT)
--------------------------------------------------

OR MORE MODERN

HAVING LAID EYES ON ME...WHICH IS IN 21ST CENTURY ENGLISH

HAVING MET ME IN PERSON

--------------------------------------------------
Note added at 20 hrs 39 mins (2004-05-14 16:50:24 GMT)
--------------------------------------------------

STYLISTICALLY-CORRECT TO ORIGINAL FINAL:
HAVING LAID EYES ON ME, Your Excellency may not announce me to the or at the Congress of the Americas

or whatever

--------------------------------------------------
Note added at 1 day 20 hrs 54 mins (2004-05-15 17:05:47 GMT)
--------------------------------------------------

My dearest petite Poussière....

The logic of the sentence.....convaincu par les yeux= refers to the fact the addressee is not seeing something and he is convinced of it, convaincre par les yeux means to believe something because you have seen it, right? Now, in the second part of the sentence, it\'s \"m\'annoncer\"....so It makes sense:
Because B saw A, now A says B can announce him.

RATHER THAN: Because B saw some unexplained thing, B can now announce A....

For me, it\'s logically embedded as it were..without more for unlawful carnal knowledge context!! that is...

Do you agree petite poussière?? :) Also, there is not any eet there at all...:)

--------------------------------------------------
Note added at 1 day 20 hrs 55 mins (2004-05-15 17:06:41 GMT)
--------------------------------------------------

above; corrrex= NOW seeing something

--------------------------------------------------
Note added at 1 day 20 hrs 56 mins (2004-05-15 17:08:01 GMT)
--------------------------------------------------

convaincre par les yeux= to believe something because you see it and here what is seen is the A person speaking to a B person or addressee...

În the context, "to apparaise" comes before "to be convinced".