Getis, Arthur, author
Macmillan, 1985
Buku Teks
Lebon, J. H. G., author
Hutchinson University Library, 1969
Buku Teks
Huntington, Ellsworth, author
John Wiley & Sons, 1951
Buku Teks
Huntington, Ellsworth, author
John Wiley & Sons, 1960
Buku Teks
Goodall, Brian, author
Penguin Books, 1987
Buku Referensi