234 CARNEGIE INSTITUTION OF WASHINGTON. 



case of the weaker spectra, of stars at the outer limits of the field, and of stars 

 fainter than twelfth magnitude, H and K are not always visible. Some diffi- 

 culty is, then, experienced in distinguishing between the early B and the late 

 F types, as the hydrogen lines have about the same intensity, and the principal 

 criterion is then the relative intensity of the continuous spectrum. In such 

 cases it may prove necessary to secure more strongly exposed spectra. 



Miscellaneous Investigations. 



(1) Observations of o Ceti were continued throughout the minimum of light 

 in December. The results obtained confirm the peculiarities noted at previous 

 minima. 



(2) Observations of the spectrum of Nova Aquilae, 1918, show that the 

 band X4686 has increased somewhat in strength, while only the "knobs" of 

 the bright nebular bands Ni and N2 remain. Hydrogen has nearly dis- 

 appeared. The ring surrounding the nucleus has diminished in brightness 

 until it is no longer visible. 



A spectrogram of Nova Cygni taken in October 1921 indicates that the 

 spectrum had reached the nebular stage, with strong bright bands of hydro- 

 gen, nebulium, and X4686. The continuous spectrum was very weak. 



The spectrum of T Coronae shows a marked decrease in the strength of the 

 bright hydrogen bands and X4686. 



(3) The wave-lengths of the bright lines in the stars Boss 5650, W Cephei, and 

 H. D. 42474, all of which show slight variations in light, have been measured. 

 Many of the lines correspond to those in rj Carinse, but their origin in most 

 cases is still uncertain. 



(4) Spectrograms of SS Cygni and SS Aurigse, taken at maximum of light, 

 show that their spectra are nearly continuous with faint, wide, dark bands of 

 hydrogen and helium. At minimum SS Cygni shows strong bright bands 

 20 a wide replacing the absorption bands, with possibly a trace of sharper 

 metallic lines. 



(5) Irregular variables. The spectrum of X Persei has been found to be 

 of type B with bright hydrogen lines and sharp H and K lines. R Coronae 

 has a marked c-type spectrum similar to that of the Cepheid variables and 

 has been classified as cF8. No certain variation in velocity has been detected. 



(6) Variables of the RV Tauri class. Three stars of this type of variability 

 have been observed, U Monocerotis, R Sagittae, and V Vulpeculae. All three 

 show considerable range in velocity and have the spectral characteristics of 

 high luminosity. They have been classified as cGOp, cGO, and cG5p, respec- 

 tively. U Monocerotis, and to a less degree V Vulpeculae, have exceptionally 

 weak hydrogen lines, a condition almost certainly due to the partial balancing 

 of absorption and emission in these lines. 



(7) Studies of the Algol variable SX Cassiopeiae have been continued. 

 The velocity curve shows remarkable variations in amplitude and eccen- 

 tricity, for which no explanation as yet seems sufficient. 



(8) It has been found that the bright lines of hydrogen in the Algol variable 

 TT Ophiuchi increase in strength as the light increases from minimum to 

 maximum. 



(9) V Sagittae and RS Canum Venaticorum have been observed during the 

 total eclipse of the brighter star. The spectra of the fainter stars were thus 



