perpetually vs sempiternally

perpetually

adv
  • Seeming to never end; endlessly; constantly. 

sempiternally

adv
  • In a sempiternal manner; eternally. 

  • in an everlasting manner, as to have an infinite temporal duration; as opposed to eternally or timelessly, as to exist outside time 

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