def faxen_factor(height, radius, lateral=True):
    """
    Return the relative change of the stokes drag according to Faxen's law.

    References
    ----------
    Schäffer, E., et al.
        Surface forces and drag coefficients of microspheres near a plane
        surface measured with optical tweezers.
        Langmuir 23, 3654–3665 (2007).
    """
    h = height
    r = radius
    if lateral:
        factor = 1 / (1 - 9 / 16 * r / h + 1 / 8 * (r / h) ** 3 - 45 / 256 *
            (r / h) ** 4 - 1 / 16 * (r / h) ** 5)
    else:
        factor = 1 / (1 - 9 / 8 * r / h + 1 / 2 * (r / h) ** 3 - 57 / 100 *
            (r / h) ** 4 + 1 / 5 * (r / h) ** 5 + 7 / 200 * (r / h) ** 11 -
            1 / 25 * (r / h) ** 12)
    return factor
