P. 195, line 1

The equation should be:

$\frac{d}{dt} \begin{bmatrix} \xi_1 \\ \xi_2 \\ \xi_3 \\ \xi_4 \end{bmatrix} = \begin{bmatrix} \xi_2 \\ \frac{1}{m_1} \left(-b_1 \xi_2 - k_1 \xi_1 + k_2 \xi_3 - k_2 \xi_1 + b_2 \xi_4 - b_2 \xi_2 \right) \\ \xi_4 \\ \frac{1}{m_2} \left( - k_2 \xi_3 + k_2 \xi_1 - b_2 \xi_4 + b_4 \xi_2 \right) \end{bmatrix}$