solarium vs sundial

solarium

noun
  • A room, rooftop, balcony, or terrace, used for its abundant sunlight (especially) when used as a medical treatment. 

  • Synonym of tanning salon, a room or business used for its sunlamps or tanning beds. 

sundial

noun
  • A device measuring the time of day by the position of a shadow cast by a pole or plate (gnomon) upon an engraved series of marks. 

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