var chap_array = new Array(
    ["6 - Ghost of the Sea",'6'],

    ["5 - Design",'5'],

    ["4 - Marine Mammals",'4'],

    ["3 - Hitodama",'3'],

    ["2 - The Day of Lightning",'2'],

    ["1 - Ruka",'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]);
    }
}