incessant vs perpetual

incessant

adj
  • Without pause or stop; not ending, especially to the point of annoyance. 

perpetual

adj
  • Continuing; uninterrupted. 

  • Set up to be in effect or have tenure for an unlimited duration. 

  • Lasting forever, or for an indefinitely long time. 

  • Flowering throughout the growing season. 

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