internally vs on the surface

internally

adv
  • Inwardly; spiritually. 

  • With regard to internal affairs. 

  • In an internal manner; within or inside of external limits; in an inner part or situation. 

on the surface

prep
  • apparently, outwardly; superficially 

How often have the words internally and on the surface occurred in a corpus of books? (source: Google Ngram Viewer )