bell tower vs cupola

bell tower

noun
  • A tower in which a bell (or set of bells) is hung; a belfry. 

cupola

noun
  • A dome-shaped ornamental structure located on top of a larger roof or dome. 

  • A type of furnace used for smelting. 

  • A solid formed by joining two polygons, one (the base) with twice as many edges as the other, by an alternating band of isosceles triangles and rectangles. 

  • An upward-projecting mass of plutonic rock extending from a larger batholith. 

  • A small cap over a structure that is shaped like a dome or inverted cup. 

  • A small turret, usually on a hatch of an armoured fighting vehicle. 

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