ballast vs vary

ballast

verb
  • To stabilize or load a ship with ballast. 

  • To lay ballast on the bed of a railroad track. 

  • To weigh down with a ballast. 

noun
  • Anything that steadies emotion or the mind. 

  • Heavy material that is placed in the hold of a ship (or in the gondola of a balloon), to provide stability. 

  • A material, such as aggregate or precast concrete pavers, which employs its mass and the force of gravity to hold single-ply roof membranes in place. 

  • That which gives, or helps to maintain, uprightness, steadiness, and security. 

  • device used for stabilizing current in an electric circuit (e.g. in a tube lamp supply circuit) 

  • Coarse gravel or similar material laid to form a bed for roads or railroads, or in making concrete; track ballast. 

vary

verb
  • To make of different kinds; to make different from one another; to diversity; to variegate. 

  • To embellish; to change fancifully; to present under new aspects, as of form, key, measure, etc. See variation. 

  • To be or act different from the usual. 

  • Not to remain constant: to change with time or a similar parameter. 

  • To institute a change in, from a current state; to modify. 

  • To change with time or a similar parameter. 

  • To display differences. 

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