apparition vs visual acuity

apparition

noun
  • An act of becoming visible; appearance; visibility. 

  • An unexpected, wonderful, or preternatural appearance; especially something such as a ghost or phantom. 

  • The first appearance of a star or other luminary after having been invisible or obscured; opposed to occultation. 

  • A period of consecutive days or nights when a particular celestial body may be observed, beginning with the heliacal rising of the body and ending with its heliacal setting. 

  • The thing appearing; a visible object; a form. 

visual acuity

noun
  • The sharpness of vision or sight. 

  • Strength of vision expressed on some definite scale. 

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