lines of the
series are the only ones that occur in appreciable quantities. The latter assumption is apparently not accurately fulfilled, as the
lines of Ca+ have recently been detected in the high level chromosphere.[435]
In the simple case of the Ca+ atom (neglecting the small number of atoms that are giving rise to the
lines) only two states of the atom are possible: the normal state, called by Milne the
state, and the excited, or