Assuming that the Earth was a completely rigid body, they calculated the period of Earth’s polhode wobble to be about 9–10 months.
ɐsˈuːmɪŋ ðætðɪ ˈɜːθ wʌzɐ kəmplˈiːtli ɹˈɪdʒɪd bˈɑːdi, ðeɪ kˈælkjʊlˌeɪɾᵻd ðə pˈiəɹɪəd ʌv ˈɜːθz pˈɑːlhoʊd wˈɑːbəl təbi ɐbˌaʊt nˈaɪn tˈɛn mˈʌnθs.