\magnification=\magstep2

$$
kT \sim E_{\rm ionize} = E_{\infty} - E_{1} 
$$

$$
Z = g_1 + {\sum_{j=2}^{\infty} g_j e^{-{(E_j - E_1)}/{kT}} }
$$

$$
{{N_{II}}\over{N_{I}}} = {  {{2Z_{II}}\over{n_e Z_{I}}}
             { \bigl( {{2 \pi m_e k T}\over{h^2}} \bigr) }^{3/2}
             e^{-{\chi}/{kT}}   }
$$

$$
{{N_{II}}\over{N_{I}}} = {  {{2 kT Z_{II}}\over{P_e Z_{I}}}
             { \bigl( {{2 \pi m_e k T}\over{h^2}} \bigr) }^{3/2}
             e^{-{\chi}/{kT}}   }
$$

\bye
