One of the best-known applications of the pure elements is the use of rubidium and caesium in atomic clocks, of which caesium atomic clocks form the basis of the second.
wˈʌn ʌvðə bˈɛstnˈoʊn ˌæplɪkˈeɪʃənz ʌvðə pjˈʊɹ ˈɛlɪmənts ɪz ðə jˈuːs ʌv ɹuːbˈɪdiəm ænd sˈiːsiəm ɪn ɐtˈɑːmɪk klˈɑːks, ʌvwˈɪtʃ sˈiːsiəm ɐtˈɑːmɪk klˈɑːks fˈɔːɹm ðə bˈeɪsɪs ʌvðə sˈɛkənd.