var chap_array = new Array(
    ["18 - Volume 4 Chapter 18",'18'],

    ["17 - Volume 4 Chapter 17",'17'],

    ["16 - Volume 3 Chapter 16",'16'],

    ["15 - Volume 3 Chapter 15",'15'],

    ["14 - Volume 3 Chapter 14",'14'],

    ["13 - Volume 3 Chapter 13",'13'],

    ["12 - Volume 3 Chapter 12",'12'],

    ["11 - Volume 2 Chapter 11",'11'],

    ["10 - Volume 2 Chapter 10",'10'],

    ["9 - Volume 2 Chapter 9",'9'],

    ["8 - Volume 2 Chapter 8",'8'],

    ["7 - Volume 2 Chapter 7",'7'],

    ["6 - Volume 2 Chapter 6",'6'],

    ["5 - Volume 1 Chapter 5",'5'],

    ["4 - Volume 1 Chapter 4",'4'],

    ["3 - Volume 1 Chapter 3",'3'],

    ["2 - Volume 1 Chapter 2",'2'],

    ["1 - Volume 1 Chapter 1",'1']
);
for (var i=0; i<chap_array.length; i++) {
    document.getElementById('id_chapter_1').options[i] = new Option(chap_array[i][0],chap_array[i][1]);
    if (document.getElementById('id_chapter_2')) {
        document.getElementById('id_chapter_2').options[i] = new Option(chap_array[i][0],chap_array[i][1]);
    }
}