var nuova
function newWindow(bookgif,title,size1,size2) {
	var1=(screen.width-size1)/2;
	var2=(screen.height-size2)/2;
	if (nuova && !nuova.closed) {
			nuova.close()
	}
	nuova = window.open(bookgif, title,'scrollbars=yes,width='+size1+',height='+size2+',left='+var1+',top='+var2+'')
}