convergence vs digression

convergence

noun
  • The evolution of similar structures or traits in unrelated species in similar environments; convergent evolution. 

  • A meeting place. 

  • The hypothesis that poorer economies' per capita incomes tend to grow faster than richer economies. 

  • The intersection of three electron beams for red, green and blue onto a single pixel in a CRT. 

  • The coordinated focusing of the eyes, especially at short range. 

  • The merging of distinct technologies, industries, or devices into a unified whole. 

  • The act of moving toward union or uniformity. 

  • The process or property of approaching some limiting value. 

digression

noun
  • An aside, an act of straying from the main subject in speech or writing. 

  • The act of straying from the main subject in speech or writing, (rhetoric) particularly for rhetorical effect. 

  • An elongation, a deflection or deviation from a mean position or expected path. 

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