function validate_email() {
   if (document.book.email.value.indexOf('@',0)==-1 ||
       document.book.email.value.indexOf('@',0)== 0 ||
       document.book.email.value.indexOf('.',0)==-1) {
    alert('\nInvalid email address.')
    document.book.email.select()
    document.book.email.focus()
    return false
    }
   }