[Pg 173] The star Canum Venaticorum has been the subject of extensive work.[466][467] The chief point of interest concerning it is the occurrence of lines ascribed to the rare earths.[468] The spectra of these elements are so rich in lines that spurious coincidences are certain to occur, but comparisons with the spectrum of Cygni and of the chromosphere suggest that the strongest lines of europium and terbium are indeed represented. From general ionization principles it would appear that enhanced spectra are probably involved, but until series relations are known it is not possible to discuss the subject further. The super-giant, or c-star, Cygni, Class , has probably greater possibilities for the stellar spectroscopist than any other star, as its spectrum is peculiarly rich in fine sharp lines, many of which are unidentified, Cygni is representative of a large class of stars, but it is the only one of them that has an apparent magnitude bright enough to render it readily accessible. The spectrum has been tabulated by Lockyer[469] and by Wright.[470] At the temperatures concerned, the doubly enhanced lines of the metals are to be anticipated, and it is probable that many of the faint unidentified lines in the spectrum of this star are those of twice ionized metallic atoms. The strongest doubly enhanced lines of the metals fall, as is well known, in the ultra-violet, Cygni contains the lines of the series of neutral helium, the most persistent lines of the element, and this is significant in view of the extremely low pressure that is assigned to the atmosphere of the star on the basis of absolute magnitude. THE C-STARS The c-characteristic was first used by Miss Maury[471] to designate stars, found in several spectral classes, that have marked spectral peculiarities. The intensities of some of the metallic lines, chiefly [Pg 174] those of ionized atoms, are greatly strengthened for the class, and other lines, chiefly those of the neutral atom, are weakened. The band becomes markedly discontinuous, and heavy blends at 4072, 4077, become conspicuous. The spectrum of a c-star is unmistakable in appearance. TABLE XXVI Wave Lenght Wave Lenght Atom Series Wave Lenght Wave Lenght Atom Series 3758.8 3757.68 Ti+ 4325.2 4314.98 Ti+ 3759.30 Ti+ 4321.1 Ti+ 3856.2 4337.6 4337.92 Ti+ 3863.2 4374.7 Ti+? 3900.7 3900.53 Ti+ 4395.3 4395.04 Ti+ 3913.6 3913.45 Ti+ 4400.2 4399.77 Ti+ 4003.0 4002.09 Fe+ 4417.9 4417.71 Ti+ 4009.4 4444.0 4443.80 Ti+ 4012.6 4012.40 Ti+ 4450.6 4450.49 Ti+ 4024.8 4025.13 Ti+ 4469.5 4468.14 Ti+ 4028.5 4028.35 Ti+ 4471.8 4472.93 Fe+ 4030.8 4409.6 4489.21 Fe+ 4053.8 4053.84 Ti+ 4491.6 4491.41 Fe+ 4077.9 4077.71 Sr+ 4501.5 4501.27 Ti+ 4122.8 4122.64 Fe+ 4508.5 4508.29 Fe+ 4128.1 4128. Si+ 4515.4 4515.34 Fe+ 4131.4 4131. Si+ 4520.3 4520.24 Fe+ 4143.9 4522.9 4522.64 Fe+ 4173.6 4173.47 Fe+ 4534.2 4533.97 Ti+ 4179.5 4178.87 Fe+ 4534.17 Fe+ 4l87.6 4556.0 4555.90 Fe+