hereupon vs on the fly

hereupon

adv
  • Immediately afterwards; at this. 

on the fly

adv
  • Spontaneously or extemporaneously; done as one goes, or during another activity. 

  • While in the air, without having touched the ground. 

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