MOUNT WILSON SOLAR OBSERVATORY. 271 



An application to the M and later K types gives marked evidence of 

 the two groups of giant and dwarf stars, no M stars occurring within 

 an interval of about 7 magnitudes. Further, in the giant stars the 

 hydrogen and the enhanced hues are relatively strong and the low- 

 temperature hnes are faint ; in the dwarf stars the reverse is the case. 



The continuous spectrum of large and small proper-motion stars 

 studied with the aid of absolute magnitude determinations confLnns 

 previous results. The violet region is relatively stronger in the low- 

 luminosity stars, the relative intensity being nearly proportional to the 

 absolute magnitude. 



The spectrum of the short-period Cepheid RR Lyrse varies between 

 types B9 and F2 during the 13-hour period of the hght variation. A 

 detailed study of all existing photometric measures shows oscillations 

 in the range of variation and in the shape of the light-curve, as well as 

 complicated changes in the length of the period. 



Periodic variations in the spectrum of SCephei are shown by 

 objective-prism spectra and by high-dispersion slit spectrograms. 

 The latter also show numerous differences in the spectra between 

 maximum and minimum of hght which indicate a temperature varia- 

 tion as well as a probable change of pressure in the star's atmosphere. 



Seventeen Cepheid variables have been found from objective-prism 

 photographs to vary in spectral type with variation in light. 



The radial velocity of the nucleus of the spiral nebula N. G. C. 4594 

 is +1,180 km., a result in good agreement with that obtained by 

 Slipher. 



^Measurements extending to a distance of 120" on either side of the 

 nucleus show a rotational velocity, or a relative motion along the arms 

 of the spiral, of 335 km. This motion varies uniformly with the dis- 

 tance from the nucleus. 



A parallax of the order of 0T0002 is obtained for the nebula on the 

 assumption that the radial motions correspond to the angular displace- 

 ments observed in Messier 101. 



The spectrum of the nucleus of the spiral nebula Messier 33 is con- 

 tinuous with absorption lines of type A. A condensation at a distance 

 of 10' from the nucleus shows a bright line spectrum, and a relative 

 velocity between nucleus and condensation of about 200 km. is indi- 

 cated by the measurement of the photographs. 



From a study of electric-furnace spectra of calcium, strontium, 

 barium, and magnesium clear evidence has been obtained of a relative 

 strengthening of the violet members of a series at higher temperatures 

 in the case of both line and band spectra. 



The banded spectra occurring in sun-spots and ascribed to titanium 

 oxide, magnesium hydride, and calcium hydride have been obtained 

 with high intensity in the furnace, and the conditions most favorable 

 for their production have been studied. 



