Observations of interstellar Ca I lines.

Evaluation of interferometric, photoelectric scans of the interstellar Ca I line at 4226 A for four stars having strong interstellar Ca II K-lines. The Ca I line is detected in three, and possibly all four, cases, of which one was kn*wn previously. Negative Ca I results are also obtained for six stars with weaker K-lines. The significance of the resulting electron densities deduced from the Ca I and Ca II lines is discussed.