Tertia means harmonising a melodic line by adding parallel 3rds to it.
Mozart-Allegro D major
Composition with extensive use of Tertia Quiescenza, that is direct motion 3rds to a melodic bass with a Quiescenza voice (pedal tone) on tonic or/and dominant added. Mozart embellishes this voice with an acciacatura.
Also check ‘Mama’ by P.I. Tschaikowsky. Same technique. When ascending the scale with Tertia Quiescenza, a progression from Tritto 22.214.171.124 to Finale 126.96.36.199 is almost automatically generated (when descending: Reverence 188.8.131.52 followed by Prinner 184.108.40.206).