A. Kirsher had suggested, in the seventeenth century, that the liturgical language of the native Christian confession in Egypt, Coptic, was the last stage of the Ancient Egyptian language.
The Abbot Barthélémy had already suggested in the eighteen century that the cartouches enclosed royal names. Thus, after the Rosetta stone had been found, Akerblad and Young were able to read some Greek and Roman royal names. Champollion, using his knowledge of the Coptic language, proved that the phonetic system wasn't only used for foreign names, thus getting the clue that allowed him to translate quite accurately many texts during the ten years that followed his discovery.
Seeing the name , he thought that was a sign for the sun, in Coptic, ``Ra''; he knew from the Rosetta stone that was associated with the words ``to give birth'', ``mose'', so he thought it was the consonant ``m'', and he knew, from Ptolemaic names, that was an ``s''. So he got : ``ra-m-s-s'', Ramesses. The same system, on the cartouche gave him the name ``Tuthmosis''. Actually, he was wrong when he thought of as an ``m'', because it is a biliteral sign for ``ms''. But this wasn't a hindrance and his system allowed him to go on. As a matter of fact, in ptolemaic times, the number of signs that could be used as uniliteral signs was so great that it was quite natural to think of the system as composed of uniliteral consonantic signs, ideograms, and determinatives.