employ vs exert

employ

verb
  • To use (somebody for a job, or something for a task). 

  • To hire (somebody for work or a job). 

  • To make busy. 

noun
  • The state of being an employee; employment. 

exert

verb
  • To make use of, to apply, especially of something non-material. 

  • To put in vigorous action. 

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