280 ROYAL SOCIETY OF CANADA 



This will occur when the convections from the interior of the star are 

 accelerated, the disturbed and therefore brighter regions giving character 

 to the spectrum, and at the same time the brightness of the star will in- 

 crease : when the convections are most rapid the wave-lengths will be least 

 and the star nearly at its brightest, and as the velocity of the convection 

 currents declines the wave-lengths of the spectral lines increase and the 

 luminosity of the star diminishes. A lessening of pressure will increase 

 the brightness and decrease the wave-lengths simultaneously. Curves 

 representing light-variations and spectral line shifts or changes in wave- 

 length due to atmospheric disturbances will resemble each other in gen- 

 eral and agree fairly closely, in point of time, in their maxima and 

 minima : maximum luminosity and minimum wave-length occurring at 

 nearly the same time as also minimum brightness and maximum wave- 

 length. 



§6. Periodicity in the variations of stars has been generally at- 

 tributed to one of the two periods met with in astronomy, namely, axial 

 rotation and orbital revolution. In the case of sun-spots it has been 

 suggested that the sun's rotation may perhaps introduce periodic changes 

 in its atmosphere, and again that the periodicity may be due to the 

 action of the planets revolving about the sun in their various periods. 

 The former explanation rests on theoretical considerations^, while the 

 latter hypothesis has some observational evidence in its favor^ and it is 

 quite evident that the changing attraction of a satellite would introduce 

 changes of pressure in the atmosphere and even though these changes 

 were slight yet they might be sufficient to cause considerable changes in 

 the established radial and transversal currents. It is conceivable also, 

 that the satellite may establish rotation or accelerate it in the equatorial 

 belt as in the case of the sun. Let it then be assumed that the phenom- 

 ena exhibited by variable stars are caused by changes in their convection 

 currents resulting from the changing action of satellites. The action of 

 a satellite changes in magnitude and direction when its orbit is eccentric, 

 and in direction only when the orbit is circular. If the satellite revolves 

 in an eccentric orbit the changes in the currents probably do not respond 

 immediately to the increasing attraction of the satellite and do not de- 

 crease proportionately with the lessening of the attraction. In other 

 words it takes an appreciable time for changes in the velocity and char- 

 acter of the convections to become established; and in addition to this 

 there is the induced effect following each change. 'This is illustrated in 



1 Wilczynski, Astrophysical Journal, 7, 124-130, 1S98 ; Moulton, Ibid., 29, 

 257-280. 1909. 



2 Wolf, Monthhi Notices. 19. 85-86, 1859: 25. 216-218. 1865. De La Rue 

 Stewart and Loewy. Ihid.. 25. 104-106 and 11.5-116. 1865; 26, 74-76. 1S66 ; 27. 

 12-14. 1867; 29, 141. l'-6'». Brown. Ihid. 60. 509-606. 1900. 



