function hidePictures( ) {

    hide('storia01');
    hide('storia02');
    hide('storia03');
    hide('storia04');
    hide('storia05');
    hide('storia06');
    hide('storia07');
    hide('storia08');
    hide('storia09');
    hide('storia10');

}
function updateStoriaBox( ) {

    var storiabox = o('storiabox');
    var st = storiabox.scrollTop;

    hidePictures( );

    if ( st >= 0 && st < 400 ) {
        show('storia01');
    } if ( st >= 400 && st < 800 ) {
        show('storia02');
    } if ( st >= 800 && st < 1200 ) {
        show('storia03');
    } if ( st >= 1200 && st < 1600 ) {
        show('storia04');
    } if ( st >= 1600 && st < 2000 ) {
        show('storia05');
    } if ( st >= 2000 && st < 2400 ) {
        show('storia06');
    } if ( st >= 2400 && st < 2800 ) {
        show('storia07');
    } if ( st >= 2800 && st < 3200 ) {
        show('storia08');
    } if ( st >= 3200 && st < 3600 ) {
        show('storia09');
    } if ( st >= 3600  ) {
        show('storia10');
    }

}