ðiːz wɜː dɪskˈʌvɚd, bˌʌt nˌɑːt pˈʌblɪʃt, baɪ tʃˈɑːɹlz sˈændɚz pˈɛɹs ɚɹˈaʊnd wˈʌn θˈaʊzənd ˈeɪthˈʌndɹɪd ˈeɪɾi, ænd ɹˌiːdɪskˈʌvɚd ˌɪndᵻpˈɛndəntli ænd pˈʌblɪʃt baɪ hˈɛnɹi ˈɛm. ʃˈɛfɚɹ ɪn nˈaɪntiːnhˈʌndɹɪd θˈɜːtiːn.
These were discovered, but not published, by Charles Sanders Peirce around 1880, and rediscovered independently and published by Henry M. Sheffer in 1913.