Не удается преобразовать тип данных - C#

private void calculateButton_Click(object sender, RoutedEventArgs e)
        {
            double number = 10;
            double newton, guess, guess2 ;
            guess = number / 2;
            guess2 = ((number / guess) + guess) / 2;
            newton = ((number / guess2) + guess2) / 2;
            string newton1;
            string.Parse(newton, out newton1);

        }