secret ballot vs show of hands

secret ballot

noun
  • The voting system involving ballots available only at official polling places, prepared at public expense, containing the names of all candidates, and marked in secret at the polling places. 

show of hands

noun
  • A vote in which people raise a hand in order to state their agreement with something. 

How often have the words secret ballot and show of hands occurred in a corpus of books? (source: Google Ngram Viewer )