plodding vs slogging

plodding

noun
  • Slow, laborious progress. 

adj
  • Progressing slowly and laboriously. 

slogging

noun
  • An act or an instance of slogging or working laboriously. 

  • A beating or thrashing. 

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