The Spectra of Variables of the RV Tauri and Yellow Semiregular Types.

Spectrograms of low dispersion and photometric observations have been obtained for a number of variables of the RV Tauri and yellow semiregular types. A revised list of members of the RV Tauri class is given, together with a preliminary description of certain spectroscopic similarities of the members of the class. A division of the RV Tauri stars into two groups is suggested. A period-luminosity relationship is found for some kinds of variable stars located in globular clusters. Attention is called to the remarkable spectroscopic variations of AC Her. The latter appears to be related to the carbon stars.