Microfiche. Although It Is Recognized That Certain Portions Are Illegible, It Is Being Released in the Interest of Making Available as Much Information as Possible

The effective level of line formation for spectroscopic absorption lines has long been regarded as a useful parameter for determining average atmospheric values of the quantities involved in line formation. The identity of this parameter has recently been disputed. Here we re-establish the dependence of this parameter on the average depth where photons are absorbed in a semi-infinite atmosphere and show that the mean depths derived by others are similar in nature and behavior.